fix(services): bind ChatAgentOpenAPIServer agents to API-key owners - #4363

ChatAgentOpenAPIServer kept every agent in one flat registry keyed by a
client-chosen agent_id, and every agent-scoped handler only checked
existence — never who was asking (issue camel-ai#4352, BOLA). Any client could
enumerate the full agent inventory via list_agent_ids, read any agent's
history (system prompts, tool results), reset its memory, or delete it;
the defect persisted even behind an authentication layer because
handlers never bound an agent to an identity.

- add api_keys to ChatAgentOpenAPIServer: requests must present a
  configured key via 'Authorization: Bearer <key>' or 'X-API-Key'
- agents are owned by the key that created them (only key hashes are
  stored); history/step/astep/reset/delete return 404 across owners
  without disclosing existence, and list_agent_ids is scoped to the
  caller's own agents
- secure by default: with no api_keys configured the server mints one
  ephemeral key (exposed as .api_key); pass api_keys=[] explicitly for
  the legacy unauthenticated single-user mode
- cross-owner /init conflicts return 409 instead of silently adopting
  the existing agent
- update the existing tests to authenticated clients and add coverage:
  401 paths, bearer/header auth, inventory scoping, cross-owner 404s,
  secret non-disclosure, 409 conflicts, ephemeral-key and open modes

Fixes camel-ai#4352

The CodeQL check run crashed at startup (failed in 5s) while the
CodeQL Advanced workflow itself passed all Analyze jobs; this empty
commit re-triggers the analysis so the check re-registers.

CodeQL's sensitive-data hashing rule also flags the HMAC variant, and
the owners map gained little from hashing anyway: the configured keys
already live in memory for authentication. Ownership now records the
validated key itself, agent-scoped checks use constant-time
hmac.compare_digest, and no hash of key material is computed anywhere.

Subagent review findings on this branch:

- non-ASCII X-API-Key/Authorization values raised TypeError inside
  hmac.compare_digest (str form is ASCII-only), turning a malformed
  request into a 500; keys are now compared as UTF-8 bytes so any
  wire value is a clean 401
- concurrent /init calls with the same agent_id raced between the
  existence check and the registry write (model construction takes
  long enough) and could double-register across owners; the
  check -> create -> register sequence is now serialized by a lock
- the official example was broken by the auth change (bare TestClient
  got 401); both example sites now present server.api_key and document
  the api_keys option

Also: 401 responses carry WWW-Authenticate: Bearer (RFC 6750), the
open mode logs a warning at startup, list_agent_ids iterates a
snapshot with constant-time owner comparison, delete uses pop with
defaults, and new tests cover non-ASCII keys, authenticated-but-
missing agents, open-mode shared identity, and the 401 header.

Review findings credit: subagent adversarial review.