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>

apps/web/lib/mcp/context.ts

@@ -9,6 +9,12 @@ import type { AuthenticatedClaims } from "@/lib/auth/jwt";
  * Resolves (or creates) the internal `users` row from the Authentik OIDC
  * claims so tools work with stable UUID foreign keys rather than raw `sub`
  * strings.
+ *
+ * `groups` and `defaultProjectKey` are populated by the MCP route handler
+ * (Agent A's work): groups come from the JWT's `groups` claim cross-
+ * checked against the `user_groups` table; defaultProjectKey is the value
+ * of the `X-Project-Key` header attached to the inbound request, used as
+ * a fallback when a tool call doesn't include `project` explicitly.
  */
 export interface UserContext {
   /** Internal users.id UUID. */
@@ -20,6 +26,19 @@ export interface UserContext {
   /** Optional profile fields if present in the access token. */
   email: string | null;
   name: string | null;
+  /**
+   * Group names this user belongs to (from the OIDC `groups` claim,
+   * cross-checked against `user_groups`). Drives sharing authorization;
+   * empty means the user is only a member of their own private projects.
+   */
+  groups: string[];
+  /**
+   * Default project key from the inbound MCP request's `X-Project-Key`
+   * header. Tools that accept a `project` argument fall back to this
+   * when none is provided so a Claude Code session pre-pinned to a repo
+   * doesn't have to repeat it on every call.
+   */
+  defaultProjectKey?: string;
 }
 
 export async function userContextFromClaims(claims: AuthenticatedClaims): Promise<UserContext> {
@@ -56,8 +75,17 @@ export async function userContextFromClaims(claims: AuthenticatedClaims): Promis
       .where(and(eq(users.oidcIss, claims.iss), eq(users.oidcSub, claims.sub)))
       .limit(1);
     if (!existing[0]) throw new Error("user upsert failed and not found on re-read");
-    return { userId: existing[0].id, sub: claims.sub, iss: claims.iss, email, name };
+    return {
+      userId: existing[0].id,
+      sub: claims.sub,
+      iss: claims.iss,
+      email,
+      name,
+      groups: [],
+    };
   }
 
-  return { userId, sub: claims.sub, iss: claims.iss, email, name };
+  // `groups` is left empty here; Agent A's MCP route handler widens it
+  // with the JWT's `groups` claim after this base context resolves.
+  return { userId, sub: claims.sub, iss: claims.iss, email, name, groups: [] };
 }