Expose execution phase and orphaned inbound diagnostics

[zzz163519]

Summary

Add an additive execution_phase to project-view comms so callers can distinguish queueing, provider execution, reply delivery, and a conservatively detected orphaned inbound task without changing the existing mailbox_state contract.

This is the diagnostic-only first step discussed in #260 and #262. It does not automatically cancel, retry, or terminalize any job.

Changes

• expose queued, executing, reply_queued, reply_delivering, orphaned, and terminal phases with a machine-readable reason;
• classify only request-anchored provider_prompt_idle recovery candidates as orphaned;
• include correlated inbound event, attempt, mailbox, and lease evidence for orphaned_active_inbound;
• make maintenance prefer orphaned_active_inbound over the lower-level provider-idle reason;
• cache inbound lookups alongside the existing project-view comms lookups.

Existing mailbox_state, business status, and recovery behavior remain unchanged.

Verification

• 120 passed — test/test_ccbd_project_view.py and test/test_maintenance_heartbeat.py
• 9 passed, 67 deselected — dispatcher reply-delivery/mailbox integration subset
• python -m py_compile for changed Python modules and tests
• git diff --check

Addresses #262.
Provides the non-destructive diagnostic foundation for #260.

[zzz163519]

CI note: the full Tests matrix is currently red on upstream main as well. The latest main run (29558401022) and this PR's Ubuntu 3.10 job both fail in the unchanged lifecycle test test_ccbd_stop_all_does_not_run_post_shutdown_heartbeat (destroy_events == []), after the rest of the suite passes. This failure is outside this PR's diff; the PR-specific targeted/smoke checks are reported in the description.