Loki Mode

CRITICAL trust fix + adoption empty-state + cleanup

• Evidence Receipt no longer reads green on a checks-free build
  (autonomy/lib/proof-generator.py): a build that produced a non-empty diff but
  ran ZERO tests, ZERO build, and passed ZERO quality gates could emit a
  "VERIFIED WITH GAPS" headline. A non-empty diff is a PREREQUISITE for VERIFIED,
  not a positive fact of passage - code was written but nothing was shown to pass.
  The diff is no longer counted as a verified fact; such a build is now honestly
  NOT VERIFIED. A genuine pass is unchanged, and a verified-but-degraded build is
  still VERIFIED WITH GAPS. One headline codepath, so this covers both the bash
  and Bun routes. Regression test added.
• Dashboard first-run empty state (dashboard-ui): a brand-new user with no
  builds now sees a "Start your first build" hero (with loki quickstart and the
  zero-key loki tour) instead of a blank, gated to a genuinely never-built
  project and fail-safe hidden on any error (never falsely claims you have not
  built).
• Actionable pre-build errors (autonomy/run.sh): a non-writable workspace
  (disk full / permissions / read-only) now fails fast with a copy-paste remedy;
  a build that produced no file changes gets an honest next-step instead of a
  silent no-op. loki tour added to help.
• Removed dead bin/postinstall.js (no postinstall hook since v7.4.12).