Add Managed Agents memory stores page to claude-api skill (#1014)

Add shared/managed-agents-memory.md covering the Memory Stores public
beta under managed-agents-2026-04-01: object model (memstore_/mem_/
memver_), create + seed, attach via resources[] at session-create time,
FUSE mount at /mnt/memory/<store>/, host-side CRUD with create-by-path
vs update-by-id, content_sha256 preconditions, and versions/redact.

Wire it through all cross-references: SKILL.md beta-headers namespace
and reading guide; api-reference SDK method rows, delete/archive quirks
bullet, AddResource note, and three new endpoint sections; core.md
architecture diagram and resources[] enumerations; environments.md
Resources intro; overview.md beta-headers table, Reading Guide row, and
archive-is-permanent bullet.

skills/claude-api/shared/managed-agents-core.md

@@ -21,7 +21,7 @@ Agent (config) ───────▶│  (agent loop: Claude + tool calls)
 Environment (template) ──▶ Container (tool execution workspace)
                                  │
                          Session ─┤
-                                 ├── Resources (files, repos — mounted at startup)
+                                 ├── Resources (files, repos, memory stores — attached at startup)
                                  ├── Vault IDs (MCP credential references)
                                  └── Conversation (event stream in/out)
 ```
@@ -83,7 +83,7 @@ Key fields returned by the API:
 | `archived_at` | string | ISO 8601 timestamp (nullable) |
 | `environment_id` | string | Environment ID |
 | `agent` | object | Agent configuration |
-| `resources` | array | Attached files and repos |
+| `resources` | array | Attached files, repos, and memory stores |
 | `metadata` | object | User-provided key-value pairs (max 8 keys) |
 | `usage` | object | Token usage statistics |
 
@@ -119,7 +119,7 @@ const session = await client.beta.sessions.create(
 | `agent`         | string or object | **Yes** | String shorthand `"agent_abc123"` (latest version) or `{type: "agent", id, version}` |
 | `environment_id`| string   | **Yes**  | Environment ID                                 |
 | `title`         | string   | No       | Human-readable name (appears in logs/dashboards) |
-| `resources`     | array    | No       | Files or GitHub repos, mounted to the container at startup |
+| `resources`     | array    | No       | Files, GitHub repos, or memory stores, attached to the container at startup. Memory stores are session-create-only (not addable via `resources.add()`). |
 | `vault_ids`     | array    | No       | Vault IDs (`vlt_*`) — MCP credentials with auto-refresh. See `shared/managed-agents-tools.md` → Vaults. |
 | `metadata`      | object   | No       | User-provided key-value pairs                  |