docs: define the allowed pull request label set (ownership, vibe-coded, language, dependencies) (#282)

[SamuelHassine]

Summary

Defines the allowed pull request label set so it can never be misread (by a human or an automated reviewer). A PR carries only:

• exactly one ownership label — filigran team or community;
• optionally vibe-coded — an AI-assisted change the author reviews before requesting others' review (added as a global label);
• the automatic language labels (javascript / python / java / go / rust / typescript) and dependencies (GitHub/Renovate).

Primary type labels (feature / bug / documentation), area/scope labels and workflow/triage labels stay issue-only and must never be added to a PR.

Updated .github/LABELS.md, .github/labels.yml, and the CONTRIBUTING conventions block.

Closes #282

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 70.34%. Comparing base (d0f50d2) to head (207fa67).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #283   +/-   ##
=======================================
  Coverage   70.34%   70.34%           
=======================================
  Files          49       49           
  Lines        1966     1966           
=======================================
  Hits         1383     1383           
  Misses        583      583           

Flag	Coverage Δ
connectors	70.34% <ø> (ø)

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