feat(computer-use-mcp): add tool lane hygiene advisory (#1919)

## Summary

Adds advisory-only tool lane hygiene inside `services/computer-use-mcp`.

This tracks the most recent non-exempt tool lane and appends a
non-blocking advisory when a registered tool is called from a different
active lane. The change is intentionally scoped to computer-use MCP
server registration and run state.

## Boundary

- Only touches `services/computer-use-mcp`.
- Does not touch app, renderer, overlay, extension, or root project
governance files.
- Does not include local AI config, local worktree artifacts,
screenshots, tokens, account identifiers, or raw environment dumps.

## Validation

Sanitized evidence is committed in
`services/computer-use-mcp/validation/tool-lane-hygiene.md`.

Ran:

- `pnpm install --ignore-scripts --frozen-lockfile`
- `pnpm -F @proj-airi/computer-use-mcp exec vitest run
src/server/tool-lane-hygiene.test.ts --config ./vitest.config.ts`
- `pnpm -F @proj-airi/computer-use-mcp exec vitest run
src/server/tool-lane-hygiene.test.ts
src/server/register-tools-coordinate-contract.test.ts
src/server/register-tools-pty-approval.test.ts --config
./vitest.config.ts`
- `pnpm exec moeru-lint --fix
services/computer-use-mcp/validation/tool-lane-hygiene.md
services/computer-use-mcp/src/server/tool-lane-hygiene.ts
services/computer-use-mcp/src/server/tool-lane-hygiene.test.ts
services/computer-use-mcp/src/server/register-tools.ts
services/computer-use-mcp/src/state.ts`
- `git diff --check`

`pnpm -F @proj-airi/computer-use-mcp typecheck` is currently blocked by
existing baseline errors in `chrome-session-manager` and
`desktop-grounding`, outside this patch. The validation note lists the
error classes without local paths or raw logs.