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>

overlay/Config/Bridge.cfg

@@ -57,6 +57,31 @@ AdminReasonMaxLength=400
 # Clamp on a timed ban's duration, seconds. A ban with no/zero duration is indefinite.
 AdminBanMaxDurationSec=31536000
 
+# Account provisioning (docs/PROTOCOL_2.md Part A). Which side may mint game accounts:
+#   website — the website is the authority; pair with Accounts.AutoCreateAccounts=false
+#             (else an in-game login of any new name still mints an account).
+#   game    — the game server is the authority; website account.create is refused.
+#   hybrid  — either side may create (the default).
+# The bridge governs only the account.create verb; the in-game first-login auto-create is
+# the core Accounts.AutoCreateAccounts setting, which you pair with the mode above. On boot
+# the bridge warns if the two contradict. An unrecognized value here falls back to 'game'
+# (the safest — no website creation).
+SignupMode=hybrid
+
+# Master switch for the account.create verb. Absent, it follows the mode (on unless
+# SignupMode=game). Set explicitly to force it on or off regardless of mode.
+AccountCreateEnabled=true
+
+# Fail closed if account.create omits a usable browser IP. The per-IP cap
+# (Accounts.AccountsPerIp) only means something if a missing/loopback IP is refused rather
+# than waved through. Turn off only for a deployment that deliberately does not cap website
+# signups by IP (MaxAccountsPerIP still applies in-game either way).
+RequireIpForCreate=true
+
+# Length caps on a website-supplied username / password, checked before the account is made.
+AccountNameMaxLength=16
+AccountPasswordMaxLength=30
+
 # The test scaffolding in tools/scaffolding/ reads its own flags from this file
 # (SeedOnStart, CensusOnStart, ProbeOnStart). They are absent here on purpose:
 # Config.Get returns the default of false when a key is missing, so a deployed