feat(protocol2): website account provisioning & unlinking (Part A)

Adds the account-provisioning plane from docs/PROTOCOL_2.md Part A: the
website can create game accounts and unlink them, gated by a shard-wide
signup mode. The existing [link flow is unchanged.

Overlay:
- BridgeConfig: SignupMode (website|game|hybrid, default hybrid; unrecognized
  falls back to game), AccountCreateEnabled (mode-following default),
  RequireIpForCreate, name/password caps, and a boot warning when the core
  Accounts.AutoCreateAccounts setting contradicts the mode.
- BridgeAccounts (new): account.create (mode gate, actor required, char-safety
  mirrored from AccountHandler, collision check, per-IP cap via CanCreate/
  LogAccess with fail-closed missing/loopback IP, create + WebsiteUserId link,
  account.audit; password never logged or echoed) and account.unlink (Owner
  floor via BridgeAdmin.Protected, clears the tag).
- BridgeAccountLink: in-game [unlink command, emits account.unlinked.
- BridgeAdmin: Protected / ResolveTargetAccount promoted to public for reuse.

Sidecar:
- POST /accounts/create, DELETE /link/:account, respond_account status mapping
  (409 collision / 429 ip cap / 403 disabled|protected / 404 not-linked / 400).
- store.record_unlink drops the mirrored link row.
- PROTOCOL_VERSION -> 2 (outbound events additive; new endpoints need v2).

Docs: INTEGRATION.md protocol bump, account.* events, endpoints, 409/429;
PROTOCOL_2.md Part A marked built.

Verified: sidecar cargo check clean; overlay compiles in the full ServUO
Scripts tree (0 errors, 0 warnings). Live end-to-end run still pending.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

sidecar/src/store.rs

@@ -104,6 +104,16 @@ impl Store {
         Ok(row.map(|r| r.get::<String, _>("website_user_id")))
     }
 
+    /// Drops the mirrored link row so event attribution stops immediately, without waiting on the
+    /// shard. Returns the number of rows removed (0 if the account was not linked here).
+    pub async fn record_unlink(&self, account: &str) -> anyhow::Result<u64> {
+        let res = sqlx::query("DELETE FROM links WHERE account = ?")
+            .bind(account)
+            .execute(&self.pool)
+            .await?;
+        Ok(res.rows_affected())
+    }
+
     pub async fn cache_profile(
         &self,
         serial: &str,