docs: bring the documentation set up to 0.14.0 (#94)

Three cross-cutting documents did not mention @vymalo/opencode-otel at
all despite it being a published plugin, and three still described the
tsc build that oxc replaced.

- architecture.md gains otel as the suite's only observer: the hooks and
  events it subscribes to, that its single mutation is a traceparent
  fetch wrapper rather than an auth one, and how it flushes without a
  dispose hook.
- security.md gains its posture: no content capture, unconditional
  credential stripping from git remotes, credential-helper stdout never
  logged, machine-and-project identity rather than developer, and the
  cardinality and egress switches.
- troubleshooting.md gains five symptom-keyed entries, all citing event
  names verified against source.
- The otel package README covers the credential helper, export-failure
  visibility and repository metadata, which all postdate it.
- README, CONTRIBUTING, docs/browser.md now describe the oxc build, and
  CONTRIBUTING states the isolatedDeclarations authoring rule — every
  export needs a locally-readable type — which was written down nowhere
  a contributor would look.

Corrections found while verifying rather than assumed:

- The hook count was wrong everywhere, including in a released changelog
  entry. Docs said otel observes "5 of 19" hooks; it has observed 9
  since 0.13.0, when chat.params, permission.ask,
  experimental.text.complete and experimental.compaction.autocontinue
  were added. Counted from the returned hook object and the Hooks
  interface, not copied from prose. The 16-of-32 event figure checked
  out.
- CONTRIBUTING told maintainers to tag the commit and publish a GitHub
  Release. The repo deliberately has neither — releases are a
  publish.yml dispatch — so following it would have done the one thing
  CLAUDE.md forbids. It also listed five published packages; there are
  eight.
- README called the suite "five small plugins" in three places.
- GETTING_STARTED linked to README#all-three-together, which does not
  exist; the heading is "Stacking the belt". Verified the emoji-heading
  anchor against GitHub's rendered output rather than guessing the slug.

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>