fix: change appname to neoirc and default DB to /var/lib/neoirc/state.db

- Change Appname from "chat" to "neoirc" in cmd/chatd/main.go
- Change default DBURL from file:./data.db to file:///var/lib/neoirc/state.db
  in both internal/config/config.go and internal/db/db.go fallback
- Create /var/lib/neoirc/ directory in Dockerfile with proper ownership
- Update README.md to reflect new defaults (DBURL, docker run example,
  SQLite backup/location docs)
- Remove stale data.db reference from Makefile clean target

The DB path remains configurable via DBURL environment variable.

Closes #44

README.md

@@ -1645,7 +1645,7 @@ directory is also loaded automatically via
 | Variable           | Type    | Default                              | Description |
 |--------------------|---------|--------------------------------------|-------------|
 | `PORT`             | int     | `8080`                               | HTTP listen port |
-| `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`. |
+| `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) |
 | `MAX_HISTORY`      | int     | `10000`                              | Maximum messages retained per channel before rotation (planned) |
 | `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. |
@@ -1667,7 +1667,7 @@ PORT=8080
 SERVER_NAME=My Chat Server
 MOTD=Welcome! Be excellent to each other.
 DEBUG=false
-DBURL=file:./data.db?_journal_mode=WAL
+DBURL=file:///var/lib/neoirc/state.db?_journal_mode=WAL
 SESSION_IDLE_TIMEOUT=24h
 ```
 
@@ -1685,8 +1685,7 @@ docker build -t chat .
 
 # Run
 docker run -p 8080:8080 \
-  -v chat-data:/data \
-  -e DBURL="file:/data/chat.db?_journal_mode=WAL" \
+  -v chat-data:/var/lib/neoirc \
   -e SERVER_NAME="My Server" \
   -e MOTD="Welcome!" \
   chat
@@ -1722,7 +1721,7 @@ make build
 
 # Run
 ./bin/chatd
-# Listens on :8080, creates ./data.db
+# Listens on :8080, writes to /var/lib/neoirc/state.db
 ```
 
 ### Reverse Proxy (Production)
@@ -1763,8 +1762,8 @@ seconds to accommodate long-poll connections.
   string). This allows concurrent reads during writes.
 - **Single writer**: SQLite allows only one writer at a time. For high-traffic
   servers, Postgres support is planned.
-- **Backup**: The database is a single file. Back it up with `sqlite3 data.db ".backup backup.db"` or just copy the file (safe with WAL mode).
-- **Location**: By default, `data.db` is created in the working directory.
+- **Backup**: The database is a single file. Back it up with `sqlite3 /var/lib/neoirc/state.db ".backup backup.db"` or just copy the file (safe with WAL mode).
+- **Location**: By default, `state.db` is created in `/var/lib/neoirc/`.
   Use the `DBURL` env var to place it elsewhere.
 
 ---