[AZ-486] F7 endpoint builders + STC-ARCH-02 (cycle 1 close)

Single source of truth for every /api/<service>/... URL the UI talks to:
src/api/endpoints.ts (25 typed builders) re-exported via the F4 barrel.
Migrates 13 production callsites in admin / annotations / flights /
settings / dataset / auth / api-client / FlightContext / DetectionClasses
to endpoints.* . Adds the STC-ARCH-02 static gate (--mode=api-literals
in scripts/check-arch-imports.mjs, wired into scripts/run-tests.sh)
that fails any new hardcoded /api/<service>/ literal in src/ outside
endpoints.ts and *.test.tsx? files.

Tests: +36 contract assertions in src/api/endpoints.test.ts (every
builder, character-identical), +6 STC-ARCH-02 architecture cases in
tests/architecture_imports.test.ts (single / double / template literal
fail paths, *.test.* exemption, line-comment skip, migrated codebase
pass). Fast profile 167 -> 209 PASS / 13 SKIP / 0 FAIL, +42 new,
0 regressions. Static profile 31 / 31 PASS.

Closes architecture baseline finding F7. Cycle 1 of Phase B closed.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/components/DetectionClasses.tsx

@@ -2,7 +2,7 @@ import { useEffect, useState } from 'react'
 import { useTranslation } from 'react-i18next'
 import { MdOutlineWbSunny, MdOutlineNightlightRound } from 'react-icons/md'
 import { FaRegSnowflake } from 'react-icons/fa'
-import { api } from '../api'
+import { api, endpoints } from '../api'
 // classColors lives under 06_annotations until F3 moves it to its own home.
 // Importing through the 06_annotations barrel would create a cycle
 // (DetectionClasses -> 06_annotations barrel -> AnnotationsPage -> DetectionClasses).
@@ -33,7 +33,7 @@ export default function DetectionClasses({ selectedClassNum, onSelect, photoMode
   const [classes, setClasses] = useState<DetectionClass[]>([])
 
   useEffect(() => {
-    api.get<DetectionClass[]>('/api/annotations/classes')
+    api.get<DetectionClass[]>(endpoints.annotations.classes())
       .then(list => setClasses(list?.length ? list : FALLBACK_CLASSES))
       .catch(() => setClasses(FALLBACK_CLASSES))
   }, [])