feat(claude): add forward_host_credentials support

Reads the host's Claude OAuth session key from ~/.claude.json at launch
and forwards it only to the egress sidecar (never to the agent), placing
a placeholder CLAUDE_CODE_OAUTH_TOKEN in the agent env so Claude Code
starts without seeing the real credential.

Mirrors the existing Codex forward_host_credentials flow (PRD 0029).
Adds claude_auth.py to extract and validate the sessionKey, a
CLAUDE_HOST_CREDENTIAL_TOKEN_REF constant in egress.py, and updates
manifest_agent.py to allow the flag for both 'codex' and 'claude'
templates. Also adds a mutual-exclusion check that rejects setting
both auth_token and forward_host_credentials together.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

bot_bottle/egress.py

@@ -29,6 +29,7 @@ if TYPE_CHECKING:
     from .manifest import ManifestBottle
 
 CODEX_HOST_CREDENTIAL_TOKEN_REF = "BOT_BOTTLE_CODEX_HOST_ACCESS_TOKEN"
+CLAUDE_HOST_CREDENTIAL_TOKEN_REF = "BOT_BOTTLE_CLAUDE_HOST_ACCESS_TOKEN"
 
 EGRESS_HOSTNAME = "egress"
 
@@ -397,6 +398,7 @@ class Egress(ABC):
         )
 
 __all__ = [
+    "CLAUDE_HOST_CREDENTIAL_TOKEN_REF",
     "CODEX_HOST_CREDENTIAL_TOKEN_REF",
     "EGRESS_HOSTNAME",
     "EGRESS_ROUTES_FILENAME",