feat(plugin): add plugin init command and developer kit (F111)

[pocky]

Summary

• Introduce awf plugin init <name> to scaffold a complete, production-ready operation plugin repository from a single CLI command, eliminating the manual copy-and-adapt workflow previously required to create new plugins
• Distinguish distribution name (awf-plugin-example) from runtime plugin id (example) consistently across the CLI, docs, example plugin, and generated scaffold so authors understand the two-name model before writing any code
• Fix awf plugin enable to accept distribution names (e.g. awf-plugin-example) by auto-resolving to the runtime manifest id, so the first-run sequence works without requiring users to know the internal name
• Align the awf-plugin-echo reference example to match the generated operation template exactly so authors can read the example as the canonical scaffold contract

Changes

Plugin Init Command

• internal/interfaces/cli/plugin_init_cmd.go: New awf plugin init <name> Cobra command with --kind, --output, and --force flags
• internal/interfaces/cli/plugin_init_options.go: Flag and argument parsing, distribution name validation (awf-plugin- prefix, lowercase ASCII pattern), runtime id derivation, kind validation (operation only, single-kind enforcement), output path normalization
• internal/interfaces/cli/plugin_init_generate.go: Repository generation pipeline: render templates, pre-flight conflict detection (including symlink traversal rejection), atomic file writes with 0644/0755 permissions, next-steps output
• internal/interfaces/cli/plugin_init_template.go: Template rendering infrastructure; resolves AWF module version and optional local replace directive for the generated go.mod
• internal/interfaces/cli/plugin_init_templates.go: Embedded Go text templates for all generated files (main.go, main_test.go, plugin.yaml, Makefile, examples/demo.yaml, README.md, AGENTS.md, .github/workflows/release.yml, go.mod)
• internal/interfaces/cli/plugin_cmd.go: Register newPluginInitCommand() in the plugin subcommand tree; fix plugin enable to normalize distribution names to runtime ids

Pack Resolver

• internal/interfaces/cli/pack_resolver.go: Add isExistingWorkflowFile helper; treat paths that resolve to existing files as local workflows even when they contain slashes (enables awf run examples/demo.yaml)
• internal/interfaces/cli/config.go: Add newWorkflowRepositoryForIdentifier to build a repository scoped to the parent directory of a local file path

Reference Example Plugin

• examples/plugins/awf-plugin-echo/main.go: Align implementation to the generated operation template contract: sdk.NewErrorResult for unknown operations and missing text, sdk.GetString for both inputs, structured output map including output key
• examples/plugins/awf-plugin-echo/main_test.go: Rewrite tests to match the generated template test style: source-reading assertions, manifest validation via pluginmgr.NewManifestParser(), Makefile target and content checks, demo workflow YAML parsing
• examples/plugins/awf-plugin-echo/Makefile: Add test, lint, install-local, uninstall-local, package, checksums targets; use dist/ build output; adopt awf-plugin-<name>_<version>_<os>_<arch>.tar.gz archive naming
• examples/plugins/awf-plugin-echo/examples/demo.yaml: Add demo workflow calling echo.echo (runtime id, not distribution name)

Tests

• internal/interfaces/cli/plugin_cmd_test.go: Add acceptance tests for plugin init full file set, --kind validation, --output, --force, invalid names, help output, and plugin enable distribution-name normalization
• internal/interfaces/cli/plugin_init_generate_test.go: Generation pipeline tests covering missing directory creation, existing directory coexistence, conflict detection ordering, symlink rejection, --force overwrite, file mode enforcement, and next-steps output format
• internal/interfaces/cli/plugin_init_options_test.go: Unit tests for parsePluginInitOptions, derivePluginRuntimeID, validatePluginInitKind, normalizePluginInitOutput, and all validation error shapes
• internal/interfaces/cli/plugin_init_template_internal_test.go: Internal template rendering unit tests
• internal/interfaces/cli/plugin_init_template_test.go: External template rendering tests covering generated file content contracts
• internal/interfaces/cli/plugin_init_docs_test.go: Generated README.md content contract tests covering first-run sequence, manifest field documentation, SDK API coverage, Makefile target documentation, and future-kind exclusion
• internal/interfaces/cli/pack_resolver_test.go: Add test for existing file path treated as local workflow despite containing slashes
• tests/integration/cli/plugin_init_test.go: Integration tests exercising the full plugin init → plugin enable → plugin list --operations flow
• tests/integration/cli/plugin_init_release_test.go: Integration tests for release asset naming convention compatibility between generated make package/make checksums output and awf plugin install expectations

Documentation

• docs/getting-started/first-plugin.md: New end-to-end tutorial: scaffold → test → install → enable → run demo
• docs/user-guide/commands.md: Add awf plugin init reference section with arguments, flags, description, examples, first-run sequence, and error table; sort plugin subcommands alphabetically; fix release asset naming convention to include <version> component
• docs/user-guide/plugins.md: Add "Create a Plugin" section with awf plugin init quick start; replace hand-written minimal plugin example with scaffold-first guidance; replace GoReleaser YAML block with generated release workflow instructions; add sdk.OperationSchemaProvider to SDK helpers table; fix awf-plugin-echo.echo → echo.echo operation reference
• docs/README.md: Add "Build Your First Plugin" to getting-started index; update plugins page description
• README.md: Add awf plugin init to command reference table; sort plugin subcommands alphabetically; mention awf plugin init in Plugin System feature bullet

Infrastructure

• go.mod: Promote github.com/rivo/uniseg from indirect to direct dependency
• .specify/implementation/F107/tasks/index.json: Remove completed F107 task index (superseded)
• .zpm/kb/pr_feature_f111_plugin_developer_kit_and_onboarding/journal.lock, .../journal.wal, .../knowledge.pl: ZPM knowledge base segment for this PR
• .zpm/mounts.json: Register new PR knowledge base mount

Test plan

• Run awf plugin init awf-plugin-example --kind operation, confirm all 9 files are created (main.go, main_test.go, plugin.yaml, Makefile, go.mod, README.md, AGENTS.md, examples/demo.yaml, .github/workflows/release.yml), and output shows the exact cd → make test → awf run examples/demo.yaml next-step sequence
• Run awf plugin init example and confirm exit code 1 with required-prefix validation error and no directory created; run awf plugin init awf-plugin-example --kind validator and confirm unsupported-kind error
• In the scaffolded directory: make build && make install-local && awf plugin enable awf-plugin-example && awf plugin list --operations — confirm example.echo appears; run awf run examples/demo.yaml and confirm it completes with success status
• Run unit tests: go test ./internal/interfaces/cli/... and confirm all plugin_init_* test files pass
• Run integration tests: go test -tags integration ./tests/integration/cli/... and confirm plugin_init_test.go and plugin_init_release_test.go pass

Closes #380

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Generated with awf commit workflow