feat(inception): UI — New-project modal step 2, InceptionCard on the project page, Rules tab shows excluded always-on rulebooks; REST exclusion routes (#2883, milestone 297 step 5)

- components/InceptionCard.vue: the one form, two homes — mode="create" in
  the New-project modal's second step (emits the choices; the create carries
  `inception`), mode="decide" on ProjectView for the owner of an undecided
  project (loads that project's defaults, records the decision). Always-on
  rulebooks listed checked (uncheck = exclude), others unchecked (check =
  subscribe), design system select, seed-Systems toggle (disabled once the
  project has Systems). Tokens only; modal canon (#2855); .btn-* canon.
- ProjectView: the card while undecided, one "Inheritance decided <date> via
  … · …" line after; onDecided refreshes the project.
- ProjectRulesTab: "Excluded always-on rulebooks" section with include-back.
- api/inception.ts (types, fetchInceptionDefaults, decideInception);
  api/rulebooks.ts: ApplicableRules.excluded_always_on, exclude/include
  wrappers; REST POST/DELETE /api/projects/<id>/exclusions/rulebooks/<rb>.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

frontend/src/api/rulebooks.ts

@@ -71,6 +71,8 @@ export interface ApplicableRules {
   }[];
   truncated: boolean;
   subscribed_rulebooks: { id: number; title: string }[];
+  /** Always-on rulebooks this project opted out of at inception (milestone 297). */
+  excluded_always_on: { id: number; title: string }[];
 }
 
 // ── Rulebooks ───────────────────────────────────────────────────────
@@ -181,3 +183,14 @@ export async function suppressTopicForProject(projectId: number, topicId: number
 export async function unsuppressTopicForProject(projectId: number, topicId: number): Promise<void> {
   return apiDelete(`/api/projects/${projectId}/suppressions/topics/${topicId}`);
 }
+
+// ── Always-on exclusions (milestone 297) ────────────────────────────────────
+
+export async function excludeAlwaysOnRulebook(projectId: number, rulebookId: number): Promise<void> {
+  await apiPost(`/api/projects/${projectId}/exclusions/rulebooks/${rulebookId}`, {});
+}
+
+export async function includeAlwaysOnRulebook(projectId: number, rulebookId: number): Promise<void> {
+  await apiDelete(`/api/projects/${projectId}/exclusions/rulebooks/${rulebookId}`);
+}
+