feat: report notifications (email + webhook) and comms package refactor

[oliverm91]

Summary

Adds the ability for a finished ProcessExecutionReport to notify itself
through one or more channels (HTML email over SMTP, or JSON webhook), and
reorganizes all communication code into a dedicated comms/ package along the
way. Runtime dependencies stay at zero (aiosmtpd is a test-only dev
dependency).

What's new (public API)

• ProcessExecutionReport.notify(*channels, only_errors=False, tasks=None, show_warnings=True)
  • only_errors=True restricts the payload to ERRORED tasks.
  • tasks=[...] restricts to the named tasks, compared case-insensitively
    (None = all, [] = none); composes with only_errors.
  • A failing channel never aborts the others; failures surface as a
    UserWarning unless show_warnings=False.
• ReportChannel (abstract) — delivers a complete report once, after the run.
• EmailChannel / WebhookChannel are now dual-capability: a
  NotificationChannel (streaming per-task failure alert) and a
  ReportChannel (one-shot report). The same instance can serve both roles.
• ReportContent(show_traceback=True, show_traced_vars=True) — per-channel,
  shareable selection of how much detail a report notification includes.
• ProcessExecutionReport.to_json() — lossless JSON of the whole report.

report = process.run()
report.notify(EmailChannel(smtp_cfg), only_errors=True)
report.notify(WebhookChannel(webhook_cfg), tasks=["fetch_orders", "Decode_Payload"])

Architecture refactor (behavior-preserving)

The communication layer was split out of the flat top-level namespace into a
comms/ package, with the domain depending only on abstract ports:

• comms/base.py — NotificationChannel, ReportChannel, ReportContent (ports).
• comms/channels.py — EmailChannel, WebhookChannel, _FileChannel (adapters).
• comms/_email.py / comms/_webhook.py — renderers + transports + handlers.
• comms/_logfile.py, comms/_error_context.py, comms/email_config.py,
  comms/webhook_config.py, comms/themes/.

Supporting changes:

• Broke an import cycle at the root — TaskStatus / TaskResult /
  TaskDependency moved to a leaf task_types.py, and ErrorData to a leaf
  error_data.py, so the comms renderers import them directly instead of the
  previous status-.value string workaround.
• De-duplicated transport — one _SMTPTransport and one _WebhookTransport
  are shared by the streaming handler and the one-shot report sender.
• Unified logger teardown — Task.close_handlers(); Process no longer
  reaches into task.logger.handlers in two places.

Full rationale and the staged plan are in arquitectura.md (incl. an
"as-built" section noting deliberate deviations; Phase 3 — splitting
render/transport into separate files — was intentionally skipped).

Testing

• Email send tests now run against a real in-process SMTP server
  (aiosmtpd, tests/conftest.py::smtp_server) and assert on what is actually
  received — headers, MIME, decoded HTML body — instead of mocking smtplib.
  Streaming tests assert an exact received count (the streaming emit
  swallows errors, so a loose check would pass on a silent no-send).
• Pure render-matrix tests (9 style×palette × 6 languages) are kept as fast unit
  tests of the template engine.
• New: report dispatch + filtering (only_errors, tasks), webhook report
  payload, content flags, and a manual inspection script
  (tests/manual_tests/manual_report_notify.py).

Verification

• uv run pytest → 141 passed
• uv run mypy → clean (21 source files)
• uv run ruff check . → clean
• uv build wheel verified to ship comms/themes/ assets.
• Runtime dependencies unchanged: zero.

Notes

• aiosmtpd is added under [dependency-groups] dev only; it is not part of the
  published wheel's Requires-Dist.
• report-notifications-design.md / report-notifications-implementation.md are
  kept as point-in-time design records; the authoritative API is the docstrings
  and tests.

Type of change

• feat — new feature
• fix — bug fix
• refactor — no behavior change
• docs — documentation only
• test — tests only
• chore / ci / build