Ratchet coverage floors up to match measured coverage

Frontend floors move to 96/96/91/92 (measured 97.27/97.27/92.87/93.78)
and the backend gate to 80 (measured 83.47). Kept 1-2pp below measured so
real regressions fail without false positives on incidental drift.

These are a ratchet: raised as coverage grows, never lowered to make a
gate pass.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RXMhc9nT6sNz1SL4j8dznL

frontend/vitest.config.ts

@@ -17,14 +17,13 @@ export default defineConfig({
       provider: 'v8',
       reporter: ['text', 'lcov'],
       // Thresholds set as a regression ratchet to prevent coverage from dropping.
-      // Measured: lines 96.52%, functions 91.08%, statements 96.52%, branches 86.78%.
+      // Measured: lines 97.27%, functions 92.87%, statements 97.27%, branches 93.78%.
       // Set ~1-2pp below measured to catch real regressions without false positives.
-      // Branches set conservatively (85) as it's the weakest metric.
       thresholds: {
-        lines: 95,
-        functions: 89,
-        branches: 85,
-        statements: 95,
+        lines: 96,
+        functions: 91,
+        branches: 92,
+        statements: 96,
       },
       include: ['src/**/*.{ts,tsx}'],
       exclude: [