refactor: [ENG-2880] drop legacy flags from brv curate / brv query

These flags survived from the pre-tool-mode era when the daemon ran an
internal LLM. In tool-mode they were already no-ops — declared on the
oclif command but never read in the run() body. Cleaning up the surface
so agents stop being told about them and so the help text reflects what
the CLI actually does.

Removed from `brv curate`:
- `-d, --folder` (folder pack — agent inlines folder content into the
  topic HTML directly)
- `-f, --files` (file context — agent reads files and inlines content)
- `--detach` (curate is two cheap RPCs; nothing to detach from)
- `--timeout` (no long-running daemon LLM call to time-bound)

Removed from `brv query`:
- `--timeout` (deterministic local BM25 lookup; default 300s was
  legacy nonsense)

Migration UX: a new shared helper `assertNoRemovedFlags` scans argv
before oclif's parser runs and throws a clear migration message naming
the equivalent tool-mode pattern. Works for both strict (curate) and
permissive-parse (query) commands.

Docs updated to match: the bundled SKILL.md, brv-instructions.md,
workflow.md, and command-reference.md no longer instruct agents to use
the removed flags. Replaced the `--detach` decision rubric with the
two-call session protocol explanation.

Out of scope (intentional):
- `brv dream --timeout` and `--detach` — separate command, still
  needed; `timeout-deprecation.ts` helper stays for that path.
- Daemon-side `CurateExecutor` --files resolution code — runs on
  legacy LLM-configured projects, not reachable from tool-mode CLI
  after this commit. A separate dead-code pass.

Verified:
- npm run typecheck clean
- npm run lint: 0 errors (262 pre-existing warnings unchanged)
- npm test: 8514 passing, 16 pending, 0 failing
  (+ 8 new `removed-flags` unit cases)