feat(spaces): end-to-end shared-space sync (membership lookup + plaintext)

Closes the gap between "invite flow UI exists" and "two users in the
same space actually see each other's data". Three pieces land together
because they're meaningless without each other.

mana-auth — new internal endpoint:
  GET /api/v1/internal/users/:userId/memberships
  Returns [{organizationId, role}, ...] for the user. mana-sync uses
  this to populate the multi-member RLS session config.

mana-sync — membership lookup:
  new internal/memberships package with an HTTP client + 5 min
  per-user cache, fail-open (empty list = pre-Spaces behavior).
  Config gets MANA_AUTH_URL (default http://localhost:3001).
  Handler.NewHandler takes the Lookup. Every Push/Pull/Stream call
  now passes spaceIDsFor(userID) to Store methods.
  GetChangesSince + GetAllChangesSince extend their WHERE clause:
    WHERE (user_id = $1 OR space_id = ANY($memberSpaces))
  so co-members see each other's rows, not just the author.

apps/web — encryption skip for shared-space records:
  encryptRecord now checks record.spaceId:
    - `_personal:<userId>` sentinel OR no active shared space → encrypt
      with user master key (E2E as today).
    - Active space resolves to non-personal type AND spaceId matches
      that space → skip encryption; write lands plaintext.
  decryptRecord is unchanged because its per-field isEncrypted() guard
  already passes plaintext through.
  Phase-1 compromise: shared-space data is protected by server RLS
  only, not E2E. Phase 2 adds per-Space shared keys with per-member
  wrap — tracked in docs/plans/spaces-foundation.md.

Plus docs/plans/shared-space-smoketest.md: step-by-step Zwei-User-Test
mit erwarteten Ergebnissen und Debugging-Hinweisen bei Problemen.

Build + go test + web check all green.

Plan: docs/plans/spaces-foundation.md

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

services/mana-auth/src/index.ts

@@ -136,6 +136,29 @@ app.get('/api/v1/internal/org/:orgId/member/:userId', async (c) => {
 	return c.json({ isMember: !!member, role: member?.role || '' });
 });
 
+/**
+ * List every Space (organization) the given user is a member of. Used by
+ * mana-sync to pass the current user's space-membership list into the
+ * `app.current_user_space_ids` session setting so the multi-member RLS
+ * policy can let space co-members read each other's records.
+ *
+ * Returns a flat array of organization ids — mana-sync doesn't care
+ * about names/roles here, only the set. Cached 5 min client-side.
+ */
+app.get('/api/v1/internal/users/:userId/memberships', async (c) => {
+	const { userId } = c.req.param();
+	const { members } = await import('./db/schema/organizations');
+	const { eq } = await import('drizzle-orm');
+	const rows = await db
+		.select({ organizationId: members.organizationId, role: members.role })
+		.from(members)
+		.where(eq(members.userId, userId));
+	return c.json({
+		userId,
+		memberships: rows.map((r) => ({ organizationId: r.organizationId, role: r.role })),
+	});
+});
+
 // ─── Login Page (OIDC) ─────────────────────────────────────
 
 app.get('/login', (c) => {