feat(sharing): project shares, co-edit safety, awareness UI (Phase 4c+d+e)

Adds project-level sharing via the new project_shares table plus the
infrastructure that makes multi-user editing safe and visible.

Authorization (lib/access.ts):
  - getAccessibleProjects / getProjectAccess centralise the predicate
    used by every read and write path.
  - readableProjectIds / writableProjectIds drive listing-style queries.
  - Web UI Server Actions and pages source group memberships from the
    user_groups table so authorization works without depending on
    Agent A's session callback shape.

Optimistic locking:
  - memories + snippets gain version + last_edited_by columns. Every
    UPDATE bumps version and stamps the editor; UPDATE WHERE clauses
    require the caller's pre-fetched version, surfacing a clear
    "refresh and try again" error on lost-write races rather than
    silently clobbering.
  - MemoryUpdateInput / SnippetPutInput accept an optional version
    token.

MCP tools:
  - memory.write / .update / .delete / .get / .list / .search,
    snippet.put / .get / .list / .delete now respect shared-project
    access (read = owner | any share, write = owner | rw share).
  - project, defaults to ctx.defaultProjectKey from the X-Project-Key
    header (populated by the MCP route — Agent A's wiring).
  - project.identify returns shared projects you have access to and
    prefers an owned project on key collision, audit-logging the
    collision so an operator can debug it.
  - Tool descriptions for memory.update, memory.write, snippet.put,
    and project.identify updated with the co-edit / shared-project
    notes.

Web UI:
  - Project detail page: ownership badge, shared-with-N-groups badge,
    owner-only "Manage sharing" section (add/flip/remove shares via
    lib/share-actions.ts). Add-share is constrained to groups the
    granter is already in.
  - "Shared" chips on memory cards in /memories and /dashboard.
  - "Last edited by ..." on memory + snippet detail pages, shown only
    when the last editor isn't the row's original author so the chip
    stays informative.
  - Read-only viewers (ro shares) lose Edit/Delete affordances on
    memories and snippets.

Migration 0004_project_shares.sql adds project_shares + the two new
columns on memories and snippets; it depends on Agent A's
0003_groups.sql for the groups, user_groups, and memory_access enum.

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

packages/schemas/src/index.ts

@@ -6,6 +6,11 @@ export type MemoryScope = z.infer<typeof MemoryScope>;
 export const MemoryVisibility = z.enum(["private", "shared", "team"]);
 export type MemoryVisibility = z.infer<typeof MemoryVisibility>;
 
+// Access level a group has on a shared project. Mirrors the Postgres
+// `memory_access` enum defined by Agent A's groups migration.
+export const MemoryAccess = z.enum(["ro", "rw"]);
+export type MemoryAccess = z.infer<typeof MemoryAccess>;
+
 export const ProjectKey = z
   .string()
   .min(1)
@@ -48,6 +53,10 @@ export const MemoryUpdateInput = z.object({
   tags: Tags.optional(),
   scope: MemoryScope.optional(),
   project: ProjectKey.optional(),
+  // Optimistic-locking token returned by memory.get / memory.list. When
+  // present, the UPDATE matches on (id, version); a 0-row result means
+  // someone else edited this memory since you read it.
+  version: z.number().int().nonnegative().optional(),
 })
   .refine(
     (v) =>
@@ -123,6 +132,9 @@ export const SnippetPutInput = z
     tags: Tags.optional(),
     scope: MemoryScope.default("user"),
     project: ProjectKey.optional(),
+    // Optimistic-locking token used on the update path (when a row with
+    // this name+scope+project already exists). Ignored on first put.
+    version: z.number().int().nonnegative().optional(),
   })
   .refine(scopeProjectRefinement.check, { message: scopeProjectRefinement.message });
 export type SnippetPutInput = z.infer<typeof SnippetPutInput>;