refactor: remove unused legacy runtime and UI

[Qiyuanqiii]

Summary

Command Runtime v2 and the V2 shell are already the production paths, but unused legacy runtime builders and UI trees still remain. Remove those remnants and the tests/styles that exist only for them: 67 files, 7,523 net lines removed.

• Delete the unused Agent Kernel/Planner/Executor/Critic scaffolding, its App wiring and private Store writers, and unused tool schema/listing APIs.
• Delete retired Controlled/Host/Risk/Once request constructors and producer-only helpers. Historical tests now construct saved records directly; retained readers, record validation, migrations and shared process primitives remain in place.
• Delete eight unreachable frontend modules, dead component branches and their exclusive tests/styles. Keep the active V2 shell, Run/Session Inspector and shared settings components.
• Retire the three unused Once fingerprint namespaces and legacy settings-width key in the protocol registry; update the generated registry and architecture notes.

Validation

• Go 1.26.6: all packages and test files compiled; ten selected App/Application/HTTP/Store history and fixture tests passed, including schema 142/185 preservation and historical Host/Risk continuation.
• go test ./internal/tools -count=1
• go test ./internal/runner -run 'Test(Historical|ControlledStartSpec|ControlledExecutionReceipt|HostCommandSavedOutput)' -count=1
• cd web && npm run build
• Frontend tests covering V2, Inspector, settings, permissions, transcript and styles: 19 files / 195 tests passed.
• Protocol inventory/evolution validation and document generation against base 2012b05e94810f5f2f817492ef1b27d058f93acc; go run ./cmd/surfacecheck; git diff --check.

The full platform matrix is left to CI; local validation targets the affected behavior.

Surface governance

• No Surface is added, promoted, downgraded, deprecated, or removed.

• If the checkbox above is not applicable, every declaration below is complete and docs/convergence/surface-registry.json plus its generated inventory are included in this PR.

• Registry item(s): N/A — no Surface change.

• Target tier / transition: N/A — no Surface change.

• Entry criteria / decision: N/A — no Surface change.

• Owner: N/A — no Surface change.

• Shared Go Application contract: N/A — no Surface change.

• Authority impact: N/A — no Surface change; only unreachable producers are deleted.

• Supported platforms: N/A — no Surface change.

• Release / test evidence: N/A — no Surface change; validation is listed above.

• Compatibility strategy: N/A — no Surface change; historical records and readers are retained.

• Deprecation window: N/A — no Surface change.

• Removal / rollback plan: N/A — no Surface change; this commit can be reverted without a schema migration.

Audit

• No credentials or local runtime data are included.
• Policy, workspace, sandbox, and persistence boundaries were reviewed.
• Project documentation was updated to describe the remaining runtime and UI paths.