feat(bundler): honor angular.json externalDependencies (#146)

[lukekania]

Closes #146

Summary

• Honors angular.json's externalDependencies array. An import like import $ from 'jquery' survives as a bare ESM specifier when jquery is declared external — the runtime (browser import map, CDN loader, micro-frontend host) resolves it. The package is neither inlined nor BFS-walked by the resolver, matching @angular/build:application (esbuild --external: jquery).
• Subpath matching: declaring jquery also externalises jquery/dist/jquery.slim etc., consistent with esbuild's package-name external semantics.
• Per-configuration overrides replace the base list (matches ng build's merge order — same as how it handles e.g. budgets).

Where the change lives

• crates/project-resolver/src/angular_json.rs: parse externalDependencies (base + per-configuration override) into ResolvedAngularProject.external_dependencies.
• crates/npm-resolver/src/lib.rs: new resolve_npm_dependencies_with_externals skips externalised specifiers in both phase-1 entry resolution and the phase-2 transitive BFS. The original resolve_npm_dependencies is now a thin wrapper that passes an empty set.
• crates/bundler/src/concat.rs + rewrite.rs: new BundleInput.external_specifiers field. is_local is updated to veto externals first (so even if a specifier leaks into bundled_specifiers, externals stay bare). Lazy-chunk routing keeps externals as direct bare imports instead of folding them through ./main.js.
• crates/cli/src/main.rs: thread externals through every resolve_npm_dependencies call site; defensively strip externals from bundled_specifiers before bundling.
• packages/builder/src/build/options.ts: drop the stale "externalDependencies is currently ignored" warning.

Tests

• Unit tests for project-resolver parsing (base, empty default, configuration override).
• Unit tests for npm-resolver skipping top-level + transitive externals, and matching subpaths.
• Bundler tests that an external import survives verbatim even if bundled_specifiers contains the same name (regression guard), and that subpaths of external packages are also kept as bare specifiers.

End-to-end verification

Against test-ng-project:

• Declared "externalDependencies": ["jquery"] in angular.json.
• Added import $ from 'jquery'; and import { something } from 'jquery/dist/jquery.slim'; in src/main.ts.
• Built with NGC_RS_BINARY=…/target/release/ngc-rs npx ng build.
• dist/test-ng-project/main.js contains both imports verbatim; jquery is not installed in the fixture and the resolver silently skips it (the BFS never asks for it) — proving the second acceptance bullet.

Notes vs. issue body

• The issue lists <script type="importmap"> emission as a separate follow-up. Left out of scope — implementation here only covers "leave the bare specifier".

Test plan

• cargo build --release -p ngc-rs
• cargo test -p ngc-bundler -p ngc-npm-resolver -p ngc-project-resolver
• cargo clippy --workspace -- -D warnings
• End-to-end: add externalDependencies to a fixture, build, grep dist/main.js for the bare import.