feat(diagnostics): the issue composer — draft, review, screenshots, zip export (E16 S3)

After Stop (or at the cap, or from Settings → Diagnosztika's past sessions)
one dialog drafts the issue: title, description, the steps drafted from the
session's markers and page changes (a marker without a label is named by its
time), the environment (version, browser, system, window, language). Beside
it, what goes with it: the browser and server logs — each reviewable line by
line, an unticked line is not sent — and the screenshots, removable, with
paste / drop / pick to add more.

- it saves as it goes (debug_sessions.draft, migration 0090): the rendered
  markdown in the user's language, the excluded rows, and its own fields to
  reopen as it was; a sent session is read-only
- the zip export (issue.md, client.log, server.log, screenshots) is built
  from the saved draft by app/issues/bundle.py — the one definition the Gitea
  delivery (S4) will share; .log, not .jsonl, which Gitea refuses
- the log line's level tags and clock move to components/logLineParts so the
  review list draws a level the way both log viewers do

backend/app/models.py

@@ -619,6 +619,8 @@ class DebugSession(Base):
     # app/debugsession.py `EndReason`: stopped by the user, or past `until`.
     ended_reason: Mapped[str | None] = mapped_column(String(16))
     issue_url: Mapped[str | None] = mapped_column(String(512))
+    # The issue being written from it (E16 S3; app/debugsession.py `save_draft` holds its shape).
+    draft: Mapped[dict | None] = mapped_column(JSONB)
 
 
 class DebugScreenshot(Base):