Add plugin SDK: third-party AC_* commands via entry points

[JE-Chen]

Medium-integration batch — declarative plugin discovery (importlib.metadata entry points), full layers + tests + EN/Zh v31 docs + README.

Feature (utils/plugin_sdk, pure-stdlib)

• discover_plugins(group='je_auto_control.commands') loads each entry point's factory → merges {command_name: handler}; broken plugins skipped (logged). load_plugins registers them into the executor via add_command_to_executor. AC_list_plugins / AC_load_plugins + ac_*. Entry-point source injectable for tests. Declarative/namespaced complement to the runtime path loader.

Verification

• 6 tests pass (merge mappings, skip broken, empty, register+invoke through executor, wiring); ruff clean; radon no CC≥C; bandit clean; PySide6-free.

[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
0 new issues

View in Codacy

🟢 Metrics 22 complexity · 0 duplication

Metric	Results
Complexity	22
Duplication	0

View in Codacy

_{NEW Get contextual insights on your PRs based on Codacy's metrics, along with PR and Jira context, without leaving GitHub. Enable AI reviewer
TIP This summary will be updated as you push new changes.}

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud