feat(extensions): MCP Client、Plugin 包与受限生命周期 Hooks

[Qiyuanqiii]

Closes #104

Summary

• add a real Go MCP Client for approved stdio and pinned HTTPS Streamable HTTP servers, with discovery, health, reconnect, timeout/cancellation, capability-drift quarantine, and model-visible tool schemas
• route MCP calls through the existing Tool Gateway, Policy, approval, budget, Run/Surface/Phase/Role checks, untrusted-output sanitization, and durable Supervisor recovery ledger
• add signed plugin.v1 packages with inert staging, two-stage capability review, pinned HTTPS/Git imports, publisher trust, upgrade/rollback/revoke, audit, and Desktop/CLI/HTTP controls
• add bounded declarative lifecycle Hooks (deny, narrow, annotate, record) across tool, Run, Session, compaction, Specialist, and checkpoint boundaries
• add schema v120-v121 extension persistence alongside schema v119 UI Evidence, restart/concurrency fencing, bilingual extension documentation, OpenAPI/TypeScript contracts, and a glass-styled Desktop extension panel

Security boundaries

• Cyber Surface is excluded.
• Remote bearer credentials are resolved from the OS credential store and are never persisted or returned by HTTP/Desktop projections.
• Discovered schemas reject external/dynamic references; remote strings and results are recursively sanitized.
• Plugin Skills remain inert resources and are never auto-installed, auto-selected, or injected.
• stdio MCP is an explicit operator-approved Code/Deliver/root + full_access host capability. Its process has a minimal environment and bounded lifecycle, but it is not Docker/OS filesystem isolation.

Conflict reconciliation

• merge current main at 4fa37c5 without rewriting the PR branch history
• retain UI Evidence as schema v119, move the MCP client runtime to v120, and move Plugin/Hooks persistence to v121
• compose Extension and UI Evidence controllers, capabilities, OpenAPI contracts, TypeScript clients, documentation, and downgrade fixtures in the same runtime
• conflict-resolution merge commit: 8887138

Verification

• go test -count=1 -timeout 30m ./internal/store (866.350s locally)
• go test -race -count=1 ./internal/mcp ./internal/plugins ./internal/hooks ./internal/uievidence
• affected application, toolgateway, domain, store migration, HTTP, Desktop, browser-runtime, and Skill tests
• go vet ./...
• go mod tidy -diff
• npm test (62 files / 269 tests)
• npm run typecheck
• npm run build
• npm audit --audit-level=high (0 vulnerabilities)
• npm run check:api

CI follow-up

• use an OS-native absolute stdio fixture path so the credential-argument regression test is portable across Windows and Linux
• retain the complete uncached go test ./... suite while raising its per-package deadline from 20 to 30 minutes; the migration-heavy Store suite took 988 seconds in one hosted run and exceeded 1,200 seconds in another
• reconciled head 8887138 passed CI run 32341250820 and Desktop release run 32341250829