test: handler-level goto-def coverage for the alternate Flux registration forms

[mikebronner]

Summary

Implements #183 — extends the handler-level goto-def coverage #108 established to the two other Flux resolution paths the same handler walks but no handler-level test exercised.

Changes

• Add flux_tag_resolves_via_anonymous_component_path — drives the anonymous_component_paths registration form (Blade::anonymousComponentPath), where the registered directory IS the components dir, so <flux:button> resolves to {flux_dir}/button.blade.php with no components/ segment. The registered dir sits outside Flux's conventional fallback locations, so only the anonymous-component-path branch can produce the candidate.
• Add flux_tag_resolves_via_self_named_candidate — drives the directory-self {base}/{last}.blade.php candidate (the third file shape push_component_file_candidates emits, salsa_impl.rs), with neither the direct file nor the index.blade.php present.
• Add a flux_paths_config helper mirroring the anonymous_component_paths arm of the flux_config helper in flux_component_hover.rs.
• Extract backend_with_config so the path-form test can prime a distinct config without duplicating the LspService harness; flux_backend now delegates to it (existing call sites unchanged).
• Note the new coverage in the module doc.

Acceptance Criteria

• A new #[tokio::test] primes LaravelConfigData with anonymous_component_paths: {"flux" → abs_dir} (mirroring the flux_config pattern in flux_component_hover.rs), writes {abs_dir}/button.blade.php, calls create_component_location_from_salsa with flux:button, and asserts the GotoDefinitionResponse::Link target URI points to that file
• A new #[tokio::test] primes config with anonymous_component_namespaces: {"flux" → "components/flux"}, writes only resources/views/components/flux/button/button.blade.php (no direct button.blade.php or index.blade.php), calls the handler with flux:button, and asserts the LocationLink target is the self-named file — the third candidate ({base}/{last}.blade.php, salsa_impl.rs)
• Both new tests drive the real async handler chain create_component_location_from_salsa → resolve_component_existing_file → LocationLink through the tower_lsp::LspService harness (same approach as the four existing tests)
• cargo test --all-features passes with both new tests included; no existing tests regress

Test Plan

• cargo test --all-features flux_goto_def_handler — all 6 tests pass (4 existing + 2 new)
• cargo fmt --check clean; cargo clippy --all-features --tests no new warnings
• Full cargo test --all-features suite: all lib/main unit tests pass. The only failing integration tests locally are fixture/environment-dependent (gitignored test-project/.env + composer update-installed Fortify package) — CI bootstraps both (ci.yml), so they pass on CI. No regression from this change (diff is one test file).

Fixes #183

[mr-sherlock-holmes]

✅ Approved

Review Summary

• Test-only PR: two new #[tokio::test]s in flux_goto_def_handler.rs extending handler-level goto-def coverage to the two resolution paths #183 called out, plus a clean flux_backend → backend_with_config extraction and a new flux_paths_config helper.
• AC #1 (anonymous-component-path form) — met. flux_tag_resolves_via_anonymous_component_path primes anonymous_component_paths: {"flux" → abs_dir}, writes {flux_dir}/button.blade.php, calls create_component_location_from_salsa("flux:button"), and pins the exact target. The registered dir (packages/flux/resources/views) sits outside every Flux hardcoded fallback (resources/views/flux, vendor/livewire/flux…), so only the anonymous-component-path branch can produce the candidate — it can't pass by coincidence.
• AC #2 (self-named candidate) — met. flux_tag_resolves_via_self_named_candidate writes only resources/views/components/flux/button/button.blade.php — no direct file, no index.blade.php — so a pass proves the third candidate ({base}/{last}.blade.php, salsa_impl.rs:3185) resolved, not candidate 1 or 2.
• AC #3 (real handler chain) — met. Both tests drive create_component_location_from_salsa → resolve_component_existing_file → LocationLink through the same LspService::new harness as the four existing tests; no handler is bypassed.
• AC #4 (CI green, no regression) — met. All five checks pass (LSP test/fmt/clippy, wasm check, CodeQL ×2). Tests use disjoint TempDirs with no shared state.
• Verified independently: the refactor preserves the existing four tests' behaviour exactly; assertions pin the full absolute path; deleting either targeted production branch would fail the corresponding test. Honest coverage, not trivia.

📋 Non-blocking follow-ups

• None.

Ready for @mikebronner to merge.