feat: add editable automation descriptions

[santhiprakash]

Problem

An automation carries only a name — there is no field anywhere that describes what it does, so list/detail surfaces fall back to rendering the raw prompt as the subtitle and cards read as instructions addressed to an agent rather than a summary addressed to a person.

Implements part 1 (this repo) of OpenHands/OpenHands#16925: persist and expose an editable description.

Changes

• Migration 022_add_automation_description — nullable Text column description on automations (cross-DB: generic sa.Text, upgrade + downgrade verified on SQLite). Renumbered to 022 after main merged 021_add_run_current_phase (feat: report live run phases for dashboard visibility #388), so the chain stays single-head.
• models.py — Automation.description: Mapped[str | None].
• schemas.py — description: str | None (max_length=2000) on CreateAutomationRequest and UpdateAutomationRequest; exposed on AutomationResponse. The PATCH handler needs no change (it already setattrs everything in body.model_dump(exclude_unset=True), so an explicit null clears the field).
• router.py — create_automation passes body.description through.
• preset_router.py — same field on CreatePromptAutomationRequest / CreatePluginAutomationRequest, and both Automation(...) constructions, so template/preset-created automations can carry one.
• capabilities_router.py — "automationDescription" added to _STATIC_FEATURES, so the UI can gate the field on service version (an older service with extra="forbid" would 422 a PATCH carrying description).
• git_sync/serializer.py — description serialized into automation.yaml only when non-null, matching the existing tarball_executables reasoning: emitting description: null for automations that have none would rewrite every synced file (and its content hash) on the first cycle, pushing one no-op commit per already-synced automation.
• git_sync/loop.py — _validate_and_resolve_fields reads description back, so a git-side edit imports on the next sync cycle (both create and update paths).

Parts 2 (OpenHands/extensions manifest attribute) and 3 (OpenHands/OpenHands UI) are separate PRs per the issue's sequencing; this PR is self-contained and backwards-compatible.

Verification

• uv run pytest tests/ -q --ignore=tests/integration → 1462 passed, 0 failed (includes new tests below).
• Rebased onto main @ f1b3244 (release 1.9.0; includes chore: bump SDK to 1.44.0 #393 SDK 1.44.0 bump and feat: report live run phases for dashboard visibility #388's 021_add_run_current_phase): full suite → 1486 passed, 0 failed on SDK 1.44.0; alembic history verified single-head … → 020 → 021 → 022 with current_phase on automation_runs and description on automations, plus downgrade -1 → 021 and re-upgrade head → 022 on a scratch SQLite DB; pre-commit (ruff format/lint, pycodestyle, pyright) all pass.
• alembic upgrade head then alembic downgrade -1 against a scratch SQLite DB — column added/removed cleanly.
• uv run pre-commit run --files <all changed files> — ruff format, ruff lint, pycodestyle, pyright all pass.

New regression tests:

• tests/test_router.py — create with/without description (persisted + echoed, absent → null); 2001-char description rejected (422); PATCH sets and explicitly-null clears.
• tests/test_git_sync_serializer.py — description key omitted from automation.yaml when null; serialized when set; round-trips through deserialize_automation.
• tests/test_git_sync.py — full sync-cycle round trip: description lands in automation.yaml, and a git-side edit to it imports back into the DB on the next cycle.
• tests/test_capabilities_router.py — automationDescription advertised.

Notes

• The only pre-existing test touched is the AutomationResponse constructor fixture in tests/test_schemas.py (added description=None to the defaults dict) — additive, no assertions changed.
• Fixes [Feature]: Give automations an editable description, shown in the UI OpenHands#16925 (part 1 of 3).

HUMAN: no human review was performed on this change; authored by Santhi Prakash with AI assistance and verified as described above.