Stability checkpoint — root hygiene + SONAR doc + batch CI rule (MR !114)

Three batched fixes (per new CLAUDE.md rule "Réduire les vagues CI") :

1. Root hygiene : run.sh moved to bin/run.sh (executable + blame
   preserved). 10 doc references updated for UI-context callers ;
   5 backend-context refs preserved (deployment-{gcp,kubernetes},
   technology-stack, infrastructure, testing — those describe
   commands in the sibling mirador-service repo).
   UI root file count : 17 → 16 (cap = 15 ; CHANGELOG.md move
   deferred to next sweep, requires release-please script update).

2. SONAR_TOKEN UI doc improvement : sonarcloud silent-failing >8d
   on a 'Project not found' error. Updated the allow_failure: true
   comment with the 3 likely root causes (project deleted, token
   rotated, user-access lost) and a dated TODO 2026-05-24 so the
   shield can be removed once one of the 3 is ruled out. No code
   change : actual fix needs SonarCloud UI + CI vars edit (user
   action only).

3. CLAUDE.md rule 'Réduire les vagues CI' : codifies the
   batch-instead-of-micro-MR pattern with explicit justification
   that local build/lint catches 80% of fails ; the remaining CI
   fails are recognisable patterns easily debugged from N-commit
   batches. Saves (N-1) × 10-15 min per CI cycle batched.