fix(fqn): keep the extension in __file__ QNs so sibling files stay distinct Refs 769

[LA-10]

What does this PR do?

cbm_pipeline_fqn_compute() stripped the extension unconditionally. For sibling
component files that's the only distinguishing part, so badge.component.ts/.html/.scss
all produced the same __file__ QN and cbm_gbuf_upsert_node() merged them into one
File node. cbm_store_list_files() then returned 8 paths for 12 files, and
write_scoped_filelist() handed that short list to grep — so search_code never opened
the merged-away siblings and silently returned incomplete results.

Not Angular-specific: it's stem equality after one strip. spec.ts/stories.ts survive
because their stems differ. Same class as #495.

Fix: skip the strip for the __file__ sentinel. Symbol and module QNs unchanged.

Verification

Repro repo @ 5e39bf9, mode=full:

	before	after
File nodes / files	8 / 12	12 / 12
extension vs file_path	mismatched	matches
search_code markers	4/5	5/5

Also fixes the extension-corruption follow-up (pass_githistory upserts landing on the
merged node).

Known gaps

Module QNs still collide; File nodes still have start_line/end_line 0 so .scss matches
land in raw_matches. Happy to add repro_issue769.c for end-to-end search coverage if wanted.

[DeusData]

Thanks for the focused diagnosis and for linking the public #769 repro. I have triaged this as a high-priority 0.9.1-rc parsing/search correctness fix. The current diff has no dependency, workflow, network, credential, prompt-injection, or supply-chain concern.

The present unit coverage is not sufficient for this change:

1. Angular component sibling files (ts/html/scss) merged into one File node; search_code silently incomplete #769's existing maintainer acceptance criterion requires an end-to-end red regression that asserts one File node per .ts/.html/.scss sibling and complete search_code marker coverage. Please add that repro test; simple FQN inequality does not prove the graph and scoped file list.
2. Assert the exact new File QNs, not only pairwise inequality, and cover multi-extension names, extensionless files, and dotfiles.
3. This changes the persisted qualified_name of every File node. An unchanged existing index can retain old identities, while an incremental update can introduce new identities only for touched files. That can create a mixed graph with duplicates, stale edges, or missing lookups. Please do not implement a migration or CI expansion yet; maintainers need to choose between an explicit full-reindex compatibility boundary and a migration/versioning strategy.
4. Remove the trailing whitespace in fqn.c and the leading "# " from the PR title.

CI is still running. The identity compatibility decision remains a blocker even if it turns green.

[DeusData]

Maintainer decision: the File-QN direction is accepted, and we will use an automatic one-time full-reindex compatibility boundary rather than an in-place migration.

Please update this PR with the following scope:

1. Add the end-to-end RED regression requested above for the Angular component sibling files (ts/html/scss) merged into one File node; search_code silently incomplete #769 sibling-file corpus. It must prove distinct File nodes and complete search_code marker coverage, then turn green with the fix.
2. Add a narrow persisted index-format compatibility marker for this File-QN format change. A pre-change index must be routed through the existing full-reindex path before incremental or watcher refresh can produce mixed old/new File identities. A freshly rebuilt/current-format index must not rebuild again on the next unchanged run.
3. Add a regression that starts from a pre-change index, proves the one-time full rebuild, verifies the distinct .ts, .html, and .scss File nodes afterward, and verifies that a subsequent run does not force another rebuild. Preserve the existing ADR/project metadata behavior of the full-reindex path.
4. Keep this as a rebuild boundary; do not add an in-place node-renaming migration. Old collided databases no longer contain enough information to reconstruct every missing sibling safely.
5. Retain the exact-QN and filename-edge-case coverage requested above and fix the current lint failure from trailing whitespace.

This resolves the maintainer-owned compatibility decision. Merge review will resume against the new exact head after these correctness and upgrade-path tests are present and CI is green.