Add JSONPath querying over parsed JSON

[JE-Chen]

Data batch (from multi-agent web research; verified absent). Full layers + tests + EN/Zh v51 docs + README.

Feature (utils/jsonpath, pure-stdlib re)

• json_query / json_query_one / json_extract: a JSONPath subset over parsed JSON — $, .key, [n]/[-n], */[*], .. recursive descent, [?(@.k op v)] filters. The executor's path walker only split on . and indexed, so array-bearing API/DB responses were awkward to extract from; json_extract runs a {key: path} mapping into a flat dict.
• Executor AC_json_query / AC_json_extract (data/mapping as object or JSON string); MCP ac_*; Builder under Data.

Verification

• 11 tests pass (dotted/index/neg-index, wildcard, filter, recursive descent, query_one default, extract mapping, quoted key, no-match empty, executor round-trip, wiring, facade); ruff clean; radon no CC≥C; bandit clean; PySide6-free.
• Rebased onto dev after the multi-channel notify (Add multi-channel webhook notifications (Slack/Discord/Teams/raw) #258) merge.

[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
0 new issues

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🟢 Metrics 73 complexity · 0 duplication

Metric	Results
Complexity	73
Duplication	0

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[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