refactor(HeadlessJobManager): split to remove TooManyFunctions/complexity suppressions

[jorisjonkers-dev-agents]

Follow-up from the lint sweep (PR #5). 20 functions — extract a job registry / process lifecycle collaborator with concurrent state-transition tests. Goal: remove the localized @Suppress once split, with integration coverage. Requires a live tmux/container test env.

[jorisjonkers-dev-agents]

Ready to pick up

Current state (verified): HeadlessJobManager.kt is 411 lines with @Suppress("LargeClass", "TooManyFunctions"). Responsibilities: job registry (in-memory map), process lifecycle (start/wait/cancel), concurrent state transitions.

Expected split (per issue):

• HeadlessJobRegistry: job state map, lookup, list
• HeadlessProcessLifecycle: start process, wait for completion, cancel
• HeadlessJobManager becomes a coordinator

Acceptance criteria:

• @Suppress("LargeClass", "TooManyFunctions") removed from HeadlessJobManager.kt.
• Concurrent state-transition tests (e.g. start + cancel race, double-start idempotency).
• Note: also see issue Inject KB_AUTO_MCP_DISABLED on headless/council launch + headless durability + RunnerPodChatGenerator cleanup #11 which tracks making the job registry persistent (currently in-memory only).

File: services/agent-gateway/src/main/kotlin/…/headless/HeadlessJobManager.kt