refactor: 30-day defaults, time-based message expiry

- Change QUEUE_MAX_AGE default from 48h to 30 days (2592000s)
- Replace count-based MAX_HISTORY with time-based MESSAGE_MAX_AGE
  (default 30 days) — messages older than the configured age are
  pruned instead of keeping a fixed count per target
- Update README to reflect new defaults and time-based expiry

README.md

@@ -1795,7 +1795,7 @@ skew issues) and simpler than UUIDs (integer comparison vs. string comparison).
 - **Channels**: Deleted when the last member leaves (ephemeral).
 - **Users/sessions**: Deleted on `QUIT` or `POST /api/v1/logout`. Idle
   sessions are automatically expired after `SESSION_IDLE_TIMEOUT` (default
-  30 days) — the server runs a background cleanup loop that parts idle users
+  24h) — the server runs a background cleanup loop that parts idle users
   from all channels, broadcasts QUIT, and releases their nicks.
 
 ---
@@ -1813,7 +1813,7 @@ directory is also loaded automatically via
 | `DBURL`            | string  | `file:///var/lib/neoirc/state.db?_journal_mode=WAL` | SQLite connection string. For file-based: `file:///path/to/db.db?_journal_mode=WAL`. For in-memory (testing): `file::memory:?cache=shared`. |
 | `DEBUG`            | bool    | `false`                              | Enable debug logging (verbose request/response logging) |
 | `MESSAGE_MAX_AGE`  | int     | `2592000`                            | Maximum age of messages in seconds (30 days). Messages older than this are pruned. |
-| `SESSION_IDLE_TIMEOUT` | string | `720h`                           | Session idle timeout as a Go duration string (e.g. `720h`, `24h`). Sessions with no activity for this long are expired and the nick is released. Default is 30 days. |
+| `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     | `2592000`                            | Maximum age of client queue entries in seconds (30 days). Entries older than this are pruned. |
 | `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) |
@@ -1833,7 +1833,7 @@ SERVER_NAME=My NeoIRC Server
 MOTD=Welcome! Be excellent to each other.
 DEBUG=false
 DBURL=file:///var/lib/neoirc/state.db?_journal_mode=WAL
-SESSION_IDLE_TIMEOUT=720h
+SESSION_IDLE_TIMEOUT=24h
 ```
 
 ---
@@ -2229,7 +2229,7 @@ GET /api/v1/challenge
 
 - [ ] **Hashcash proof-of-work** for session creation (abuse prevention)
 - [x] **Queue pruning** — delete old queue entries per `QUEUE_MAX_AGE`
-- [x] **Message rotation** — prune messages older than `MESSAGE_MAX_AGE`
+- [x] **Message expiry** — delete messages older than `MESSAGE_MAX_AGE`
 - [ ] **Channel modes** — enforce `+i`, `+m`, `+s`, `+t`, `+n`
 - [ ] **User channel modes** — `+o` (operator), `+v` (voice)
 - [x] **MODE command** — query channel and user modes (set not yet implemented)

internal/config/config.go

@@ -75,7 +75,7 @@ func New(
 	viper.SetDefault("MOTD", defaultMOTD)
 	viper.SetDefault("SERVER_NAME", "")
 	viper.SetDefault("FEDERATION_KEY", "")
-	viper.SetDefault("SESSION_IDLE_TIMEOUT", "720h")
+	viper.SetDefault("SESSION_IDLE_TIMEOUT", "24h")
 
 	err := viper.ReadInConfig()
 	if err != nil {

internal/handlers/handlers.go

@@ -31,7 +31,7 @@ type Params struct {
 	Healthcheck *healthcheck.Healthcheck
 }
 
-const defaultIdleTimeout = 30 * 24 * time.Hour
+const defaultIdleTimeout = 24 * time.Hour
 
 // Handlers manages HTTP request handling.
 type Handlers struct {
@@ -205,7 +205,7 @@ func (hdlr *Handlers) runCleanup(
 }
 
 // pruneQueuesAndMessages removes old client_queues entries
-// per QUEUE_MAX_AGE and prunes messages per MESSAGE_MAX_AGE.
+// per QUEUE_MAX_AGE and old messages per MESSAGE_MAX_AGE.
 func (hdlr *Handlers) pruneQueuesAndMessages(
 	ctx context.Context,
 ) {