docs: update README for new endpoints, fix config name, remove dead field

- Document POST /api/v1/logout endpoint
- Document GET /api/v1/users/me endpoint
- Add 'users' field to GET /api/v1/server response docs
- Fix config: SESSION_TIMEOUT -> SESSION_IDLE_TIMEOUT
- Update storage section: session expiry is implemented
- Update roadmap: move session expiry to implemented
- Remove dead SessionTimeout config field from Go code

README.md

@@ -1158,6 +1158,55 @@ curl -s http://localhost:8080/api/v1/channels/general/members \
   -H "Authorization: Bearer $TOKEN" | jq .
 ```
 
+### POST /api/v1/logout — Logout
+
+Destroy the current client's auth token. If no other clients remain on the
+session, the user is fully cleaned up: parted from all channels (with QUIT
+broadcast to members), session deleted, nick released.
+
+**Request:** No body. Requires auth.
+
+**Response:** `200 OK`
+```json
+{"status": "ok"}
+```
+
+**Errors:**
+
+| Status | Error | When |
+|--------|-------|------|
+| 401    | `unauthorized` | Missing or invalid auth token |
+
+**curl example:**
+```bash
+curl -s -X POST http://localhost:8080/api/v1/logout \
+  -H "Authorization: Bearer $TOKEN" | jq .
+```
+
+### GET /api/v1/users/me — Current User Info
+
+Return the current user's session state. This is an alias for
+`GET /api/v1/state`.
+
+**Request:** No body. Requires auth.
+
+**Response:** `200 OK`
+```json
+{
+  "id": 1,
+  "nick": "alice",
+  "channels": [
+    {"id": 1, "name": "#general", "topic": "Welcome!"}
+  ]
+}
+```
+
+**curl example:**
+```bash
+curl -s http://localhost:8080/api/v1/users/me \
+  -H "Authorization: Bearer $TOKEN" | jq .
+```
+
 ### GET /api/v1/server — Server Info
 
 Return server metadata. No authentication required.
@@ -1166,10 +1215,17 @@ Return server metadata. No authentication required.
 ```json
 {
   "name": "My Chat Server",
-  "motd": "Welcome! Be nice."
+  "motd": "Welcome! Be nice.",
+  "users": 42
 }
 ```
 
+| Field   | Type    | Description |
+|---------|---------|-------------|
+| `name`  | string  | Server display name |
+| `motd`  | string  | Message of the day |
+| `users` | integer | Number of currently active user sessions |
+
 ### GET /.well-known/healthcheck.json — Health Check
 
 Standard health check endpoint. No authentication required.
@@ -1572,8 +1628,10 @@ skew issues) and simpler than UUIDs (integer comparison vs. string comparison).
 - **Queue entries**: Stored until pruned. Pruning by `QUEUE_MAX_AGE` is
   planned.
 - **Channels**: Deleted when the last member leaves (ephemeral).
-- **Users/sessions**: Deleted on `QUIT`. Session expiry by `SESSION_TIMEOUT`
-  is planned.
+- **Users/sessions**: Deleted on `QUIT` or `POST /api/v1/logout`. Idle
+  sessions are automatically expired after `SESSION_IDLE_TIMEOUT` (default
+  24h) — the server runs a background cleanup loop that parts idle users
+  from all channels, broadcasts QUIT, and releases their nicks.
 
 ---
 
@@ -1590,7 +1648,7 @@ directory is also loaded automatically via
 | `DBURL`            | string  | `file:./data.db?_journal_mode=WAL`   | SQLite connection string. For file-based: `file:./path.db?_journal_mode=WAL`. For in-memory (testing): `file::memory:?cache=shared`. |
 | `DEBUG`            | bool    | `false`                              | Enable debug logging (verbose request/response logging) |
 | `MAX_HISTORY`      | int     | `10000`                              | Maximum messages retained per channel before rotation (planned) |
-| `SESSION_TIMEOUT`  | int     | `86400`                              | Session idle timeout in seconds (planned). Sessions with no activity for this long are expired and the nick is released. |
+| `SESSION_IDLE_TIMEOUT` | string | `24h`                            | Session idle timeout as a Go duration string (e.g. `24h`, `30m`). Sessions with no activity for this long are expired and the nick is released. |
 | `QUEUE_MAX_AGE`    | int     | `172800`                             | Maximum age of client queue entries in seconds (48h). Entries older than this are pruned (planned). |
 | `MAX_MESSAGE_SIZE` | int     | `4096`                               | Maximum message body size in bytes (planned enforcement) |
 | `LONG_POLL_TIMEOUT`| int     | `15`                                 | Default long-poll timeout in seconds (client can override via query param, server caps at 30) |
@@ -1610,7 +1668,7 @@ SERVER_NAME=My Chat Server
 MOTD=Welcome! Be excellent to each other.
 DEBUG=false
 DBURL=file:./data.db?_journal_mode=WAL
-SESSION_TIMEOUT=86400
+SESSION_IDLE_TIMEOUT=24h
 ```
 
 ---
@@ -2008,11 +2066,14 @@ GET /api/v1/challenge
 - [x] Docker deployment
 - [x] Prometheus metrics endpoint
 - [x] Health check endpoint
+- [x] Session expiry — auto-expire idle sessions, release nicks
+- [x] Logout endpoint (`POST /api/v1/logout`)
+- [x] Current user endpoint (`GET /api/v1/users/me`)
+- [x] User count in server info (`GET /api/v1/server`)
 
 ### Post-MVP (Planned)
 
 - [ ] **Hashcash proof-of-work** for session creation (abuse prevention)
-- [ ] **Session expiry** — auto-expire idle sessions, release nicks
 - [ ] **Queue pruning** — delete old queue entries per `QUEUE_MAX_AGE`
 - [ ] **Message rotation** — enforce `MAX_HISTORY` per channel
 - [ ] **Channel modes** — enforce `+i`, `+m`, `+s`, `+t`, `+n`