refactor(skills): collapse installed agent skills into two routers (sol, journal)
- Project install now installs exactly two router skills — `sol` and `journal`; app talent fragments are builder source, not installed skills.
- New `sol skills build [--check]` generates deterministic, checked-in router references (solstone/talent/{sol,journal}/references/commands.md) from app fragments; `--check` is read-only and wired into install-checks/make ci via `check-skill-references`; `make skills` converges references then links.
- New shared `solstone/think/command_polarity.py` (READ_VERBS/WRITE_VERBS/classify_verb) is the single polarity oracle; check_layer_hygiene imports it.
- Removed the `vit` skill.
- `journal start` is now runtime-only — dropped the .last-start-version self-heal (wrapper/unit/skill refresh); setup/install/doctor own convergence now.
- Added examine-only advisory `skill_state` doctor check (sol + journal doctor) that warns on missing/stale/foreign router links and names the repair command.
- User-wide install now installs the `sol` skill; an existing user-wide `solstone` bundle is left untouched.
- Updated docs (SOLCLI, APPS, project-structure, CONTRIBUTING, INSTALL, AGENTS) and the journal template to the two-router contract.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>