feat(executive): executive view on the redesign layout (#903)

[alex-dembele]

Fourth screen of the redesign epic (#899). Stacked on #927 (action center): the base is feat/902-action-center, so the diff shows only this issue.

What changes for the user

The executive view is now the one-page committee summary from the mockup: "Comité des risques · T4 2026", Copier le lien and Exporter le rapport, four headline figures with their movement since last quarter, the five largest exposures (inherent and targeted residual bars), compliance by framework with the counting footnote, and the decisions the committee owes, each with Reporter and Approuver.

Backend

• POST /governance/approvals/:id/defer (migration 0071): a dated "deferred to the next committee" note; the request stays pending at the same step. Only someone eligible to sign the open step may defer, so it is never a way round maker-checker. Audit event defer.
• The daily score snapshot also keeps ALE, live critical risks and average compliance (migration 0072). /score/history returns quarter_baseline, the last snapshot before the current quarter, or null.
• The financial summary's top risks carry ale_after.
• Fix found in the live pass: UpdateRequest wrote a fixed column list without deferrals. The API answered 200, the audit said one deferral, the row stayed empty. Repository test added.

Frontend

• features/analytics/ExecutiveDashboard.tsx rewritten; the old executiveService / useExecutive are removed (nothing else imported them).
• With no snapshot before the quarter, a tile says "pas encore de relevé au trimestre précédent" rather than printing a movement nobody measured.
• Approve and Defer are optimistic, roll back on refusal, and do not retry. The app-wide mutation policy (retry: 3) sent a refused signature four times.
• A request's own description is its sub-line when present, else type and requester.

Verified

• go test ./...: all packages pass, including the new TestUpdateRequest_PersistsDeferrals (failed before the fix).
• npx tsc -b --noEmit clean, eslint clean on the touched files, npx vitest run 112 files / 1013 tests (two clean runs; one earlier run right after go test had 23 timeouts across 8 unrelated files and did not reproduce).
• New committeeDecisions.test.tsx: optimistic defer, rollback, a refused signature sent once (fails if retry: false is removed), approved state.
• Live on Postgres with the parity dataset at 1440×900, dark and light, side by side with the design: Reporter persisted and survived a reload ("Reportée le 9 oct.", moved last); Approuver on someone else's request → approved; on one's own → "Vous ne pouvez pas signer cette étape.", one request sent; Copier le lien wrote the page URL; Exporter le rapport generated the board report and opened /reports/board.

Deliberate differences from the mockup

• Risk ids read #84cb6560, not R-0142: risks have no human reference yet, and the register shows the same form.
• The compliance footnote says "Contrôles mis en œuvre sur contrôles applicables · hors non applicables". The mockup's "partiel compté pour moitié" is not how coverage is computed, so the page does not claim it.
• Exposure keeps its direction (D-067): lower is better, so "−4 pts" is green.

Not done here

• 414 px could not be checked: the headed browser will not go below 517 px. At 517 there is no horizontal scroll (the dashboard behaves the same).
• GET /analytics/executive remains on the backend with no frontend caller left. Removing it is a separate cleanup.

Closes #903