refactor: remove dashboard, flatten to single-package project

[Exelord]

Scope reset per owner direction. The dashboard server + Solid UI
subsystem (PRs #19 → #29, the entire dashboard track) was overengineered
for the actual need — CI consumption + ad-hoc developer queries
already work fine against cache.db with vzn stats or
sqlite3. This PR rips it all out and returns the project to a
single src/ at root.

Diff stats

77 files changed, 143 insertions(+), 3598 deletions(-)

Dep tree: 304 packages → 19. Test count: 286 → 248 (the dashboard
tests went with the code; everything else still passes).

What's deleted

• apps/ (the entire apps/dashboard/ Solid + Vite + UnoCSS app)
• src/dashboard.ts + src/dashboard.test.ts (the JSON API server)
• packages/run/ (the directory; src/ promoted to root)
• dashboard subcommand from cli.ts + its help text
• parseDashboardArgs, dashboardCmd, DashboardUiMissingError,
  resolveUiDir, createDashboardServer, the full set of API types
• docs/modules/dashboard.md
• docs/design/dashboard.md
• "Build dashboard UI" step from .github/workflows/ci.yml
• workspaces glob, build:dashboard script from package.json

What stays (analytics for CI, no UI)

• runs table + v11 analytics columns (run_id, cpu_ms,
  peak_rss_bytes, wallclock_start/end_ns, cache_hit,
  bytes_uploaded/downloaded)
• src/ulid.ts + hrtime span stamping in orchestrator
• Bun.spawn resourceUsage() capture in runner.ts / sandbox.ts
• vzn stats command — surfaces the same data as the dashboard
  Overview page used to
• CI scripts can also query .vzn/cache/cache.db directly with
  sqlite3 for any custom metric. The cache file IS the API.

What stays untouched

• sandbox (bwrap/sandbox-exec)
• layered-cache
• remote-cache + cache-archive (Turbo /v8/artifacts/ wire)
• workspace config loading (defineWorkspace)
• everything in vzn run

Layout

src/                    # was packages/run/src/
docs/
tsconfig.json           # was packages/run/tsconfig.json
package.json            # was packages/run/package.json (merged with root)

Test plan

• bun install clean — 19 packages
• bun run format clean
• bun run lint clean
• bun test src/ — 248 pass / 0 fail
• bun src/bin.ts --version / --help — no dashboard refs in
  help text

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