feat(#232): add /agent replan directive#

Problem#

No directive existed to reset a task's full phase state, close any open PR/branch, and restart from refinement. /agent restart was blocked on active tasks; /agent replan is needed for a clean slate restart regardless of task state.

Task / Link#

Closes #232

Changes#

• Add 'replan' to ALLOWED_DIRECTIVES in directive.dto.ts
• Add closePR() and deleteBranch() to GitHubService (404/422 treated as success)
• Add cleanupLabelsForReplan() to PhaseHooksService (removes refined, in-review, agent-blocked; adds in-refinement)
• Implement full replan handler in DirectiveService: validates state, closes PR/branch, resets phases, records event, cleans labels, enqueues refine
• Wire replan into PhaseRouterService: VALID_DIRECTIVES, resolvePhase() (returns 'refine'), directive handling block (no active-process rejection)
• Update DirectiveModule to import GitHubModule, EventModule, PhaseHooksModule

Notes#

• In-flight Claude runs are not force-killed on replan (PIDs not tracked across service boundary). The phase-router's active-phase guard prevents double-execution; old processes time out naturally.
• Replan on already-in-active-refine tasks is a no-op with an explanatory comment.
• Replan on terminal tasks (succeeded, failed, complete) is rejected with an explanatory comment.

Testing#

• Unit tests added: replan in DirectiveService (normal path, no-PR path, already-in-refine guard, terminal-state rejection, PR-close failure tolerance)
• Unit tests added: closePR and deleteBranch in GitHubService (happy path, 404/422 as success, non-404/422 rethrow)
• Unit tests added: resolvePhase with replan directive in PhaseRouterService
• npm run lint — 0 errors, 0 new warnings
• npm run test — 661/661 passing
• npm run build — clean