feat: declare module permissions

Establishes the one canonical PermissionDeclaration contract
(packages/contracts/src/authorization.ts) — id/baseline/description,
strict, unknown-property-rejecting — consumed by both Core's
authorization registry and module manifests, replacing Core's
previously separate interface.

Bumps the canonical module manifest to manifestVersion 3: permissions
become complete declarations instead of bare identifier strings, with
manifest-owned namespace and duplicate-id enforcement. Version 2 and
bare string-array permissions are rejected outright; there is no
compatibility adapter.

Adds composePlatformPermissionRegistry (core/src/modules/permissions.ts),
a pure, synchronous composer that builds one platform permission
registry from Core's own declarations plus every already-discovered
module's, in deterministic order, reusing createPermissionRegistry
and rejecting any module-contributed permission in the reserved
core.* namespace. core/src/authorization remains independent of
core/src/modules; only the module integration layer depends on
authorization.

Updates the module template, module-development docs, authorization
docs, and existing manifest fixtures for manifestVersion 3. Does not
wire the combined registry into apps/api — that is pass 2.

templates/module/ekklesia.module.json

@@ -1,5 +1,5 @@
 {
-  "manifestVersion": 2,
+  "manifestVersion": 3,
   "id": "example",
   "name": "Example Module",
   "description": "A minimal backend-only Ekklesia module template.",
@@ -14,7 +14,13 @@
       "version": "1.0.0"
     }
   ],
-  "permissions": ["example.records.read"],
+  "permissions": [
+    {
+      "id": "example.records.read",
+      "baseline": "restricted",
+      "description": "Read example records."
+    }
+  ],
   "storage": {
     "buckets": [
       {