v0.12.0

v0.12.0 - the universal mount release

The v0.12 arc: every extension mounts through one registration surface, the
old mount API retires with machine-checked proofs, and the module tier
becomes truly removable.

Universal mount

• One registration surface: MountWithAPI on agent.Plugin - all 19 modules
  mount through the ExtensionAPI beside the classic seams; no module
  reaches around the registry (core/agent split stays compiler-enforced).
• Live module toggles: the settings panel toggles modules at runtime, the
  registry introspects itself, and dismount undoes by identity (a remount
  replays its emitter hooks cleanly).

Engine ring

• Tier law made physical: http_channel/ and tui/ move to the repo root as
  the always-on ENGINE ring; core/ stays stdlib-only (import law enforced
  by test), modules/ is the toggleable tier.
• Kanban namespaces (Q10) - multi-board isolation on the workspace registry.

Retire + prove

• The classic mount stops existing: the last nine capsules mount through the
  registration surface and the old API is deleted, not deprecated.
• Binary purity is a machine, not a promise: scripts/nm-purity.sh proves
  the compiled binary carries zero module nouns for a removed capsule;
  double-boot diff and a mutation suite prove removal end to end.

Session + UX

• Sessions pin their model + workspace (composer chip, sidebar caret zone,
  '+' mints a session with a continuous placeholder).
• Retry moves to the message action row; logs is bottom-hosted only;
  fullscreen keeps the sidebars.

Fixes

• Updater: bare omega update reports N-behind and prompts; --yes installs.
• Skills loader reads <name>/SKILL.md (prod skills were invisible).
• Journey harness: orphaned headless chromes no longer poison suite runs.
• SSRF/sqlite/ephemeral hardening from the v0.10 gate wave.

Install or update: omega update (or omega update --nightly for the
nightly channel).