feat(snippets): named reusable artifacts with scope mirroring memories

Snippets are exact-name-keyed templates (PR formats, checklists, style
rules) — prescriptive artifacts the user wants applied consistently.
Distinct from memories, which are searched descriptive prose.

- Migration 0002 adds scope/project_id/deleted_at to snippets, partial
  unique indexes per scope, and a scope/project CHECK constraint
  mirroring memories_scope_project_chk.
- New @shared-memory/schemas: SnippetName/Put/Get/List/Delete inputs
  with shared scope-project refinement.
- lib/snippets.ts: get/put/list/softDelete helpers used by both the
  Web Server Actions and the MCP tool handlers.
- Four new MCP tools (snippet.put/get/list/delete) with directive
  descriptions contrasting against memory.* (exact-name lookup vs
  search; templates vs facts).
- /snippets pages: list, new, [name] with edit + delete and a
  scope-picker when a name lives in multiple scopes.
- Nav: Snippets link between Memories and Projects.

Design note: when a name exists in both user and project scope,
snippet.get without an explicit scope prefers project (if project key
given) then falls back to user. The detail page shows a picker when
the name is ambiguous and no scope query param was supplied.

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

packages/schemas/src/index.ts

@@ -65,3 +65,75 @@ export const ProjectIdentifyInput = z.object({
   display_name: z.string().min(1).max(200).optional(),
 });
 export type ProjectIdentifyInput = z.infer<typeof ProjectIdentifyInput>;
+
+// =============================================================================
+// Snippets
+//
+// Snippets are named, exactly-reproducible artifacts (templates, formats,
+// checklists). Unlike memories, they're fetched by EXACT name — never
+// searched. They mirror the memory scope/project model so the same key
+// can have a global default plus per-repo variants.
+// =============================================================================
+
+export const SnippetName = z
+  .string()
+  .min(1)
+  .max(200)
+  .regex(
+    /^[a-zA-Z0-9._\-/]+$/,
+    "snippet name may only contain alphanumerics, ._-/",
+  );
+export type SnippetName = z.infer<typeof SnippetName>;
+
+export const SnippetBody = z.string().min(1).max(64_000);
+export const SnippetDescription = z.string().max(2_000);
+
+// Shared scope/project consistency: project-scope requires `project`,
+// user-scope forbids it. Matches the DB CHECK constraint and the same
+// refinement used implicitly for memories at the handler level.
+const scopeProjectRefinement = {
+  check: (v: { scope?: "project" | "user"; project?: string }) => {
+    if (v.scope === "project") return Boolean(v.project);
+    if (v.scope === "user") return v.project === undefined;
+    return true;
+  },
+  message: "scope='project' requires `project`; scope='user' forbids `project`",
+};
+
+export const SnippetPutInput = z
+  .object({
+    name: SnippetName,
+    body: SnippetBody,
+    description: SnippetDescription.optional(),
+    tags: Tags.optional(),
+    scope: MemoryScope.default("user"),
+    project: ProjectKey.optional(),
+  })
+  .refine(scopeProjectRefinement.check, { message: scopeProjectRefinement.message });
+export type SnippetPutInput = z.infer<typeof SnippetPutInput>;
+
+export const SnippetGetInput = z
+  .object({
+    name: SnippetName,
+    scope: MemoryScope.optional(),
+    project: ProjectKey.optional(),
+  })
+  .refine(scopeProjectRefinement.check, { message: scopeProjectRefinement.message });
+export type SnippetGetInput = z.infer<typeof SnippetGetInput>;
+
+export const SnippetListInput = z.object({
+  project: ProjectKey.optional(),
+  scope: MemoryScope.optional(),
+  tags: z.array(z.string()).optional(),
+  limit: z.number().int().min(1).max(200).default(50),
+});
+export type SnippetListInput = z.infer<typeof SnippetListInput>;
+
+export const SnippetDeleteInput = z
+  .object({
+    name: SnippetName,
+    scope: MemoryScope.optional(),
+    project: ProjectKey.optional(),
+  })
+  .refine(scopeProjectRefinement.check, { message: scopeProjectRefinement.message });
+export type SnippetDeleteInput = z.infer<typeof SnippetDeleteInput>;