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/views/ProjectListView.vue

@@ -1,7 +1,9 @@
 <script setup lang="ts">
 import { ref, computed, onMounted } from "vue";
 import { useRouter } from "vue-router";
-import { apiGet, apiPost } from "@/api/client";
+import { apiGet, apiPost, apiErrorMessage } from "@/api/client";
+import { emptyChoices, type InceptionChoices } from "@/api/inception";
+import InceptionCard from "@/components/InceptionCard.vue";
 import { useToastStore } from "@/stores/toast";
 import { milestoneColor } from "@/utils/palette";
 
@@ -47,6 +49,9 @@ const newTitle = ref("");
 const newDescription = ref("");
 const newGoal = ref("");
 const creating = ref(false);
+// Step 2 of the modal (milestone 297): what the new project inherits.
+const modalStep = ref<1 | 2>(1);
+const newInception = ref<InceptionChoices>(emptyChoices());
 
 const filteredProjects = computed(() => {
   if (activeTab.value === "all") return projects.value;
@@ -73,6 +78,8 @@ function openNewProjectModal() {
   newTitle.value = "";
   newDescription.value = "";
   newGoal.value = "";
+  modalStep.value = 1;
+  newInception.value = emptyChoices();
   showNewProjectModal.value = true;
 }
 
@@ -88,13 +95,15 @@ async function createProject() {
       title: newTitle.value.trim(),
       description: newDescription.value.trim() || undefined,
       goal: newGoal.value.trim() || undefined,
+      // The decision rides the create: a project made here is never undecided.
+      inception: newInception.value,
     });
     projects.value.unshift(project);
     showNewProjectModal.value = false;
     toast.show("Project created");
     router.push(`/projects/${project.id}`);
-  } catch {
-    toast.show("Failed to create project", "error");
+  } catch (e: unknown) {
+    toast.show(apiErrorMessage(e, "Failed to create project"), "error");
   } finally {
     creating.value = false;
   }
@@ -266,8 +275,9 @@ function overallPct(project: Project): { total: number; pct: number } {
     <teleport to="body">
       <div v-if="showNewProjectModal" class="modal-overlay" @click.self="closeModal">
         <div class="modal-card">
-          <h3 class="modal-title">New Project</h3>
-          <div class="modal-field">
+          <h3 class="modal-title">{{ modalStep === 1 ? "New Project" : "New Project — what it inherits" }}</h3>
+          <InceptionCard v-if="modalStep === 2" mode="create" v-model:choices="newInception" />
+          <div v-if="modalStep === 1" class="modal-field">
             <label>Title <span class="required">*</span></label>
             <input
               v-model="newTitle"
@@ -275,11 +285,11 @@ function overallPct(project: Project): { total: number; pct: number } {
               class="modal-input"
               placeholder="Project title"
               autofocus
-              @keydown.enter="createProject"
+              @keydown.enter="modalStep = 2"
               @keydown.escape="closeModal"
             />
           </div>
-          <div class="modal-field">
+          <div v-if="modalStep === 1" class="modal-field">
             <label>Goal</label>
             <input
               v-model="newGoal"
@@ -289,7 +299,7 @@ function overallPct(project: Project): { total: number; pct: number } {
               @keydown.escape="closeModal"
             />
           </div>
-          <div class="modal-field">
+          <div v-if="modalStep === 1" class="modal-field">
             <label>Description</label>
             <textarea
               v-model="newDescription"
@@ -301,7 +311,17 @@ function overallPct(project: Project): { total: number; pct: number } {
           </div>
           <div class="modal-actions">
             <button class="modal-btn" @click="closeModal">Cancel</button>
+            <button v-if="modalStep === 2" class="modal-btn" @click="modalStep = 1">Back</button>
             <button
+              v-if="modalStep === 1"
+              class="modal-btn modal-btn-primary"
+              @click="modalStep = 2"
+              :disabled="!newTitle.trim()"
+            >
+              Next
+            </button>
+            <button
+              v-else
               class="modal-btn modal-btn-primary"
               @click="createProject"
               :disabled="!newTitle.trim() || creating"