Fix unresolved placeholders for trunk-based workflows

[sebastientaggart]

Wraps {{BRANCH_DEV}}, {{PLATFORM_COMPLIANCE_NOTES}}, and {{CONVENTIONS_NOTES}} in {{#if}} conditional blocks so they are only included when defined in the project config.

Previously, projects using trunk-based workflow (no BRANCH_DEV) or leaving compliance/conventions notes undefined would see warnings about unresolved placeholders during sync.

Issue #18

[sebastientaggart]

Review Summary

Verdict: APPROVE

Findings

No issues found. Code looks correct and follows project conventions.

The PR does two things, both correct:

1. Typo fix (CodeCanon -> CodeCannon): Consistent rename across all generated files, source skills, templates, docs, and sync.sh itself. The MARKER constant in sync.sh is updated, and the marker-line f-string matches. All adapters (claude, cursor, gemini, codex) are covered.

2. Conditional placeholder wrapping: {{BRANCH_DEV}}, {{PLATFORM_COMPLIANCE_NOTES}}, and {{CONVENTIONS_NOTES}} are wrapped in {{#if}} / {{#if !}} blocks in the source skills (start.md, review-agent.md). The syntax matches the apply_conditionals() parser in sync.sh (which expects {{#if KEY}} / {{#if !KEY}} / {{/if}} on their own lines with uppercase keys). The trunk-mode fallback in start.md correctly uses {{BRANCH_PROD}} instead. Generated output files (.claude/commands/review.md, .claude/review-agent-prompt.md, etc.) show the conditionals were resolved correctly by sync, with placeholder-free output and updated hashes where content changed.