refactor(git-gate): centralize hostname qualification in globalize_slug

Adds globalize_slug(slug) to bottle_state alongside bottle_identity.
git_gate_provision now calls globalize_slug(slug) instead of inlining
socket.gethostname(), so the hostname-qualification logic has a single,
named home. Assumes slug is a mint_slug output.

Title format changes from bot-bottle:{host}:{slug}:{name}
to bot-bottle:{host}-{slug}:{name} to match the globalize_slug contract.

bot_bottle/bottle_state.py

@@ -31,6 +31,7 @@ from __future__ import annotations
 import dataclasses
 import json
 import secrets
+import socket
 import string
 from dataclasses import dataclass
 from pathlib import Path
@@ -87,6 +88,14 @@ def bottle_identity(agent_name: str) -> str:
     return f"{slug}-{suffix}"
 
 
+def globalize_slug(slug: str) -> str:
+    """Return a globally-unique slug qualified with the current hostname.
+
+    Assumes slug is a value returned from mint_slug. Use wherever a slug
+    must be unique across hosts (e.g. deploy-key titles)."""
+    return f"{socket.gethostname()}-{slug}"
+
+
 @dataclass(frozen=True)
 class BottleMetadata:
     """Persistent record of how a bottle was launched, written at
@@ -340,6 +349,7 @@ __all__ = [
     "BottleMetadata",
     "agent_state_dir",
     "bottle_identity",
+    "globalize_slug",
     "bottle_state_dir",
     "cleanup_state",
     "clear_preserve_marker",