🔖 Release 0.13.0

[taras]

Why

main is at 0.12.1, and six pull requests have landed since 0.12.0 was
released. The manifests are the single version source — the compiled binary
reports whatever they say, and the draft release's tag follows them — so until
they move, none of that work can ship.

What changes

Before: every @executablemd manifest declares 0.12.1, the workspace entries
in bun.lock declare 0.12.1, and the site badge reads v0.12.0.

After: all three read 0.13.0.

Minor rather than patch, twice over:

• New capability. A <Session> says which model and effort level its
  conversation runs under (✨ Select the model and effort a <Session> runs under #829); workflows run from a source bundle without Git
  (✨ Execute Markdown workflows without Git (#443) #826); installations declare their own structural syntax (✨ Let installations declare structural syntax (#806) #810, ✨ Expand installed structural syntax (#806) #812); trusted
  Plugins install before a document runs (✨ Install trusted Plugins before a document runs (#818) #821); Codex launches natively through
  one materialization turn (✨ Launch Codex natively through one materialization turn (#755) #823).
• A breaking rename. 💥 Replace Authority terminology with concrete XMD concepts #820 replaced the Authority terminology with concrete
  XMD concepts, changing a public surface.

Scope

Included

• The version field of every workspace member's deno.json and
  package.json, stamped by deno task bump 0.13.0.
• The version of each @executablemd workspace entry in bun.lock, which the
  bump task deliberately does not touch (release-process-spec §2).
• VERSION in site/routes/index.tsx, the badge the site renders.

Intentionally unchanged

• packages/test-support stays at 0.0.0. It is not published, and the bump
  task does not stamp it.
• No dependency versions move. The ten 0.12.1 entries in bun.lock were all
  @executablemd members; no unrelated package shared that number.
• No behavior changes. This is the release bump and nothing else.

Generated or mechanical changes

• The twenty manifest edits come from deno task bump 0.13.0.
• The bun.lock edits are the ten workspace-member version fields, restamped
  by hand because bun install will not rewrite entries that already satisfy
  the lockfile.

How to verify it

grep -h '"version"' packages/*/deno.json | sort | uniq -c   # 10 × 0.13.0
grep -c '0\.12\.1' bun.lock                                 # 0
deno task check
deno task check:jsr
deno task lint
deno task validate:docs

After merge, publish the draft release as v0.13.0; its tag follows the
manifests.

Scope confirmation

• Every changed file supports the purpose described above.
• Unrelated cleanup and formatting changes are excluded.
• Generated or mechanical changes are clearly identified.
• The description matches the final diff and test results.