feat: rebuild task navigation and expose budget, MCP and PR workflows

[Qiyuanqiii]

Summary

Users could reach many task capabilities only through deep diagnostic pages, while task budgets, project configuration and first-time MCP authentication had no complete product workflow. This slice adds direct task navigation and shared Go-backed configuration, preserving the existing execution, approval and recovery paths.

• Organize conversation, files, terminal, preview, recovery, observation and delivery entries; connect the settings hub to the exact selected Run's GitHub tools.
• Add bounded task budget inputs, safe .prayu/config.yaml previews and pinned configuration reads. Schema v186 preserves historical creation fingerprints, binds requested/effective budgets, and keeps snapshots immutable through replay and successor Runs.
• Add presence/set/delete for manual HTTPS MCP bearer credentials through the shared Go API and OS store, with descriptor/scope binding and acknowledgment of shared references.
• Expose existing PR reply/resolve/unresolve/reviewer operations and registered Go/npm Bisect recipes through their existing preview/approval contracts.

Refs #257. This is a scoped implementation checkpoint, not completion of the entire rebuild. Docker onboarding, Plugin lifecycle/Hooks, guided UI Evidence, Batch preparation/rework and native platform acceptance remain open. Project exclusions and suggested skills/actions are explicitly recorded metadata, without automatic filtering/install/execution. See docs/FRONTEND_REBUILD_STATUS.md for boundaries and remaining work.

Validation

• Full frontend suite: 184 files / 1,822 tests passed.
• TypeScript, production build and generated OpenAPI/client checks.
• Go 1.26.9 targeted budget/project-config, creation replay, successor, v185-to-v186 migration, invalid direct insert, MCP and HTTP/OpenAPI checks; focused MCP race and injected-store Desktop checks.
• Full projectconfig, protocolregistry, surfacegovernance, releasegate and producte2e packages; protocol reader-history and Surface checks.
• go vet for all seven affected Go packages (app, application, domain, httpapi, projectconfig, store and desktop).
• Production browser against an isolated real Go process: task navigation/drafts, 390px layout, project narrowing, pinned budget after project-file edits, exact-Run GitHub entry and MCP credential absence/first-entry UI.
• Full GitHub CI matrix on f9471d33: all 22 checks passed, including Go tests/vet, all eight Store shards, authority race checks, dependency audit, TypeScript, real LSP on three platforms, Windows/macOS Desktop shells and real Edge UI evidence.

No real model, OS credential mutation, MCP discovery or remote GitHub write was performed in this browser pass. The isolated environment correctly refused new Thread creation without a configured model. Saved-budget browser verification used a CLI-created fixture; successful HTTP creation/recovery is covered by Go/client regression tests. Original browser screenshots are retained locally, not represented by generated illustrations.

Surface governance

• No Surface is added, promoted, downgraded, deprecated, or removed.
• 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: Existing CLI/HTTP/Desktop Surfaces share Go configuration, credential and review services.
• Authority impact: Go-owned scope, policy, approvals, runtime gates, credential ownership and immutable identities are retained.
• Supported platforms: Existing supported Surfaces; native cross-platform acceptance is not expanded by this PR.
• Release / test evidence: Validation above and the status document.
• Compatibility strategy: Additive API inputs, old creation fingerprints/readers retained, strict new-input bounds and compatible historical snapshot reads.
• Deprecation window: N/A — no Surface change.
• Removal / rollback plan: Preserve schema v186 and saved identities; UI entry points can be reverted without rewriting task history or credential values.

Audit

• No real credentials or local runtime data are included.
• Policy, workspace, sandbox and persistence boundaries were reviewed.
• Project memory and implementation/evidence status were updated.