workflow: project-driven agent workflow (docs-first, TODO/ROADMAP tracking, verify-before-done)

- system prompt gains a Project workflow block when the repo tracks its own
  progress (TODO.md/ROADMAP.md/docs): read the task list first and keep it
  current, spec-first for non-trivial work, complete unit tests, verify before
  declaring done
- TODO.md + ROADMAP.md loaded as 'Project tracker' instruction blocks, capped
  tighter than AGENTS.md so the agent sees the shape without drowning in it
- one soft nudge per session when a turn writes files without touching the
  task list; suppressed when todo_write was called; never a gate
- /workflow command + panel showing TODO/ROADMAP/docs presence, line/file
  counts, nudge state
- config: workflow.enabled (default true), workflow.docsDir (default docs)
- prompt-cache version key extended with wf: so toggling the workflow busts
  the cached system prompt
- docs: docs/workflow.md, configuration table row, ROADMAP + TODO entries
- tests: test/workflow.test.ts (9 tests)

830 tests pass, typecheck clean, build green, live headless demo verified

ROADMAP.md

@@ -37,6 +37,15 @@ step boundary by its own budget, complementing the session ceiling.
 **`/fork`** — clone the session at the last turn boundary into a new saved session;
 trying a different approach no longer costs the original.
 
+**Project-driven workflow** — when a repo tracks its own progress (TODO.md,
+ROADMAP.md, docs/), the agent carries a workflow policy in its system prompt:
+read the task list first and keep it current, spec-first for non-trivial work,
+complete unit tests, verify before done. TODO.md/ROADMAP.md ride along as
+`Project tracker` instruction blocks. A soft once-per-session nudge reminds an
+agent that edited files without updating the task list. `/workflow` shows the
+state; `workflow.enabled` / `workflow.docsDir` configure it. See
+[docs/workflow.md](docs/workflow.md).
+
 ### 0.1.0-beta.1
 
 **Core loop** — `streamText` with tool approvals suspended and resumed through the SDK's