feat(flags): real feature-flag system with bulk eval + operator UI

Real backend for the flags page (was pure mock). Built so it's ready for
the first risky rollout (likely the Stalwart JMAP client or the Stripe
billing engine).

services/platform-api:
- Flag schema (key, description, state, pct, scope.{plans, tenantSlugs,
  partnerSlugs, environments}, embedded history capped at 20)
- FlagsService with CRUD + evaluateAll(tenantSlug) → { key: bool }
  Eval algorithm:
    off  → false; on → true
    targeted → require non-empty scope (empty allowlist means "nobody"),
               then match every non-empty axis
    rollout  → match scope, then sha256(`${tenantId}:${key}`) % 100 < pct
  Hash-based rollout is deterministic: bumping pct only flips the new
  slice. Pure helpers (matchesScope, hasAnyScope, inRolloutBucket) are
  exported for future unit tests.
- FlagsController exposes GET /flags, GET /flags/:key, POST /flags/evaluate
  (JwtAuthGuard); POST/PATCH/DELETE require OperatorGuard. History entries
  capture the actor's email.
- SeedService idempotently creates 10 flag keys mapping to real Dezky
  concerns (jmap_native_v2, gdpr_export_v2, new_billing_engine, etc.).
  $setOnInsert so operator edits survive restarts.

apps/operator:
- 6 proxies: /api/flags index get/post, [key] get/patch/delete, evaluate post
- types/flag.ts with the shape that mirrors the backend
- pages/flags.vue: useFetch real list, row click opens FlagDetail,
  "New flag" opens NewFlagModal, scope summary column shows targeting
  at a glance
- FlagDetail.vue: side panel with segmented state, rollout slider with
  live "~N of M tenants" preview from /api/tenants, plan/tenant/env chip
  pickers, dirty-tracked Save, instant Kill-switch (PATCH state=off+pct=0),
  embedded change history
- NewFlagModal.vue: minimal create form (key + description). Everything
  else is configured in the detail panel afterward.
- CommandPalette: feature-flag rows now come from /api/flags instead of
  the dropped fixture, so newly-created flags are searchable immediately
- data/fixtures.ts: drop FLAGS / FeatureFlag exports (replaced by the
  real backend)

Smoke-tested end-to-end: list renders 10 seed flags, opening gdpr_export_v2
and flipping to rollout 25% then saving persists + adds a history entry,
kill-switch sets state=off in one click, /api/flags/evaluate returns the
correct booleans for the seeded tenant, same tenant gets the same answer
on consecutive evals (determinism), and creating + deleting a flag through
the UI roundtrips correctly.

services/platform-api/src/schemas/flag.schema.ts

@@ -0,0 +1,76 @@
+import { Prop, Schema, SchemaFactory } from '@nestjs/mongoose'
+import { HydratedDocument, Types } from 'mongoose'
+
+export type FlagDocument = HydratedDocument<Flag>
+
+export type FlagState = 'off' | 'targeted' | 'rollout' | 'on'
+
+// Embedded change log on the flag itself. Capped to the last 20 entries via a
+// guard in FlagsService — keeps the doc small and the side-panel render fast.
+export interface FlagHistoryEntry {
+  at: Date
+  byUserId?: Types.ObjectId
+  byEmail?: string
+  action: string  // e.g. 'created', 'state: off → rollout', 'pct: 25 → 50'
+  note?: string
+}
+
+@Schema({ collection: 'flags', timestamps: true })
+export class Flag {
+  // snake_case identifier used in code paths. Same regex as TenantPlan/slug-ish
+  // — keeps it greppable and unambiguous in audit messages.
+  @Prop({ required: true, unique: true, index: true, lowercase: true, trim: true })
+  key!: string
+
+  // Human label shown in the UI. Optional but recommended.
+  @Prop({ default: '' })
+  description!: string
+
+  @Prop({ enum: ['off', 'targeted', 'rollout', 'on'], default: 'off', index: true })
+  state!: FlagState
+
+  // Only consulted when state === 'rollout'. Hash-based assignment to a bucket
+  // (see FlagsService.evaluate) means a given tenant either is or isn't in the
+  // rollout — flipping the pct only changes the new slice, not existing ones.
+  @Prop({ default: 0, min: 0, max: 100 })
+  pct!: number
+
+  // Targeting axes. All optional; empty/missing = "no restriction on this axis".
+  // For state === 'targeted' / 'rollout', a tenant must match every non-empty
+  // axis to be eligible (intersection, not union).
+  @Prop({
+    type: {
+      plans: { type: [String], default: [] },
+      tenantSlugs: { type: [String], default: [] },
+      partnerSlugs: { type: [String], default: [] },
+      environments: { type: [String], default: [] },
+    },
+    default: () => ({ plans: [], tenantSlugs: [], partnerSlugs: [], environments: [] }),
+  })
+  scope!: {
+    plans: string[]
+    tenantSlugs: string[]
+    partnerSlugs: string[]
+    environments: string[]
+  }
+
+  @Prop({ type: Types.ObjectId, ref: 'User' })
+  createdBy?: Types.ObjectId
+
+  // Capped at last 20 in FlagsService.recordHistory.
+  @Prop({
+    type: [
+      {
+        at: { type: Date, default: () => new Date() },
+        byUserId: { type: Types.ObjectId, ref: 'User' },
+        byEmail: String,
+        action: { type: String, required: true },
+        note: String,
+      },
+    ],
+    default: [],
+  })
+  history!: FlagHistoryEntry[]
+}
+
+export const FlagSchema = SchemaFactory.createForClass(Flag)