sync: background job runtime, agent/plugin manager plugins, slimmer prompts

[Luhaozhu]

Syncs the community edition with the current upstream tree. 97 files, no binaries.

This supersedes #111 and #112 — it carries everything they had plus the workflow-mode
fix on the job wake-up path, so those two are being closed in favour of this one.

Background job runtime (workflow mode)

• Adds the job subsystem: orchestration/job_runtime.py, job_wakeup.py,
  core/services/job_service.py, the run_job tool, the /v1/jobs and
  /v1/internal/jobs routes, and the Job model.
• Wires it up on the CE side, which was the missing half. The tool was already
  registered and the prompts already mentioned it, but the routers were absent from
  CE_ROUTERS, the model was not exported from core/db/models/__init__.py, and no
  migration created the tables — so submitting a job answered 404 on the first
  callback and died on the spot. Adds ce_0006_job_runtime.py; the migration chain
  still has a single head.
• Runs jobs in the background by default, resolves the callback base URL instead of
  hard-coding the host, reaps orphaned jobs, and keeps timestamps timezone-aware.
• Carries workflow_chat through the wake-up round. The wake-up message tells the
  model it can run_job(action='resume'), but the wake-up path built its context from
  scratch and dropped workflow mode, so run_job was not on the tool surface and the
  model pulled every work item back into the main loop. Chat metadata is the source of
  truth, so non-workflow chats are not switched on by accident. Covered by
  tests/orchestration/test_job_wake_mode.py (terminal wake inherits the mode,
  progress wake inherits the mode, non-workflow chats stay off).
• Job progress strip above the composer, with abnormal terminal states re-fetched on
  mount so a job that died while the page was closed is still reported instead of
  looking like it never ran.

Agent manager and plugin manager plugins

• Two new marketplace plugins that move sub-agent and plugin CRUD into the chat:
  agent_manager_mcp / plugin_manager_mcp servers plus the agent-manager and
  plugin-manager bundles.
• Their route descriptions are written as prompt text rather than marketplace copy,
  since they ship on every turn.

Prompt and tool-schema slimming

• Default system prompts 5.3k → 4.0k characters, code_exec 5.3k → 4.4k, with all
  rules preserved.
• 14 MCP tool descriptions compressed: tool schemas 13.8k → 10.8k tokens (−21.5%),
  roughly 3k tokens of static prefill saved per request.

Reliability and UI

• Reverts the process-level search rate limit, which throttled the whole search MCP
  down to one call per minute.
• Fixes the sandbox session lock across event loops, so keep-alive no longer fails
  silently and leaves jobs stuck in running.
• Sidebar chat list supports drag-to-reorder; the manual order takes precedence over
  updatedAt and follows the account.
• Mobile pass: safe areas, iOS zoom, touch targets, dark top bar.

Verification

• CE derived tree built from upstream with scripts/build_ce.py; brand gate, required
  runtime files gate, forbidden artefacts gate and binary allowlist all pass.
• CE_ROUTERS — all 43 module names resolve to a file under api/routes/v1/.
• core/db/models/__init__.py — all 15 submodule imports resolve.
• Alembic — 6 migrations, single head ce_0006, job tables created.