test(matrix): misc route coverage — incidents/confirm-deletion/usage-wall/webhook-inspector/experiments (exempt→mapped)

Closes the last real-flow wave of the route-coverage tail: the five "misc"
routes that lived in route_donebar_guard_test.go's routeCoverageExemptions
with a TODO pointer and no mapped test now move exempt→mapped, backed by a new
DB-backed handler-integration suite (misc_routes_block_integration_test.go,
TestMiscBlock_*) that drives each route through the SAME middleware chain
router.go wires against a real migrated Postgres:

  - GET /api/v1/incidents              → TestMiscBlock_Incidents_PublicFeed
      public status-page feed contract ({ok,items,total,status_page}, no auth).
  - GET /auth/email/confirm-deletion   → TestMiscBlock_ConfirmDeletionRedirect_TokenBranches
      tokenized email-link redirect (token IS the credential): present token →
      302 to dashboard with token carried verbatim; missing/blank → canonical
      400 missing_token envelope.
  - GET /api/v1/usage/wall             → TestMiscBlock_UsageWall_RealDBContract
      RequireAuth chain + real Postgres: 401 unauth, near_wall=true + flattened
      metadata + cache headers, team-tier short-circuit, team-scoped isolation.
  - GET /api/v1/webhooks/:token/requests → TestMiscBlock_WebhookInspector_TokenScopedAndIsolated
      receive→store→inspect round-trip: token-as-bearer reads only its own
      captures (cross-token isolation), invalid→400, unknown→404, cross-team
      session→403.
  - POST /api/v1/experiments/converted → TestExperimentsConverted_WritesAuditRow
      already DB-backed + production-router covered by experiments_test.go; the
      row points there rather than duplicating the audit round-trip.

Helpers are prefixed misc* (no redefinition of miniRedis/doJSON/decodeBody/
requireTestDB). After the move, the remaining routeCoverageExemptions hold only
legitimately-exempt routes (OPTIONS/CORS preflight, app.All verb fan-out,
static content, GitHub-App OAuth/HMAC callbacks, internal/operator + admin-
console, SES/Brevo provider webhooks) plus the W3 billing/api-keys/audit + W4
stack-env real flows that carry their own matrix-wave TODO pointers.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: mastermanas805