feat: bounty board, task lifecycle, AI work performer flow, notifications (phase 8)

- whitelist HTML sanitizer (stdlib tokenizer) with XSS vector tests
- developer board: pool-scoped visibility, customer/search/minBounty/sort
  filters, stale-task age badges, competing-claims visibility setting,
  saved filters in profile extras
- claims: request/withdraw (developer), approve/decline (consultant) with
  notifications to winners and losers; unassign/abandon back to board
- work tracking: start, sanitized comments with @mention notifications,
  time logging, submit for review
- review queue + review with per-AC checklist stored on the timeline;
  approve writes the immutable bountyAwards row (human assignees only)
- assign-to-AI: §5.2 job submission, HMAC-verified callback endpoint,
  idempotent by jobId, artifacts downloaded into GridFS, failure path
  keeps the task assigned with timeline + notification
- notifications API + bell with unread badge, dropdown, page, WS toasts
- pages: bounty board, my-tasks kanban, task detail (role-driven actions,
  review dialog, AI dialog), review queue, developer pool

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

web/templates/my-tasks.html

@@ -0,0 +1,10 @@
+{{define "content"}}
+<h1>My Tasks</h1>
+<div class="error-box" id="error" role="alert"></div>
+<div class="kanban mt" id="kanban">
+  <section class="kanban-col" data-col="assigned"><h2>Assigned</h2><div class="stack"></div></section>
+  <section class="kanban-col" data-col="in_progress"><h2>In progress</h2><div class="stack"></div></section>
+  <section class="kanban-col" data-col="in_review"><h2>In review</h2><div class="stack"></div></section>
+  <section class="kanban-col" data-col="approved"><h2>Done</h2><div class="stack"></div></section>
+</div>
+{{end}}