chore(mypy): type database layer (src/ 42 -> 29)

[axisrow]

Part of #1133 (mypy debt reduction axis). Independent sibling of #1275 (telegram utils) — disjoint files.

mypy delta

python -m mypy src/ on this branch: 42 errors -> 29 errors (−13). No new errors in untouched files (verified against per-file baseline).

File	Errors before	After
src/database/facade.py	3	0
src/database/migrations.py	2	0
src/database/pool.py	2	0
src/database/repositories/collection_tasks.py	2	0
src/database/repositories/messages.py	2	0
src/database/connection.py	1	0
src/database/repositories/filters.py	1	0

Changes (typing-only, no runtime behavior change)

• migrations / connection / pool / repositories.filters: cast() around fetchall() / execute_fetchall() results — aiosqlite stubs declare Iterable[Row] while the runtime value is a list; cast is a runtime no-op (no copy).
• facade.transaction(): bind the asserted connection to a local db so the narrowed non-optional type is visible inside the busy-retry lambda (mypy does not propagate attribute narrowing into closures).
• facade.record_rename_event: separate write_cur variable — the read path returns BufferedCursor, the write path aiosqlite.Cursor (which owns lastrowid).
• repositories.collection_tasks: add ExportTaskPayload to _deserialize_payload return union and _serialize_payload param union — both code paths already handle it at runtime (the task_kind == EXPORT parse branch and the isinstance tuple); this only aligns annotations with existing code. The interop payloads (interop: новые типы задач + payload-модели (dm_reply/chat_answer/fetch_*) #960 DmReplyTaskPayload etc.) stay excluded per the design note in models.py.
• repositories.messages: is None or == "" narrowing before int() (semantically identical to the tuple-membership check); assert sq.id is not None inside the chunk loop — valid pre-filters None ids two lines above.

Verification

• ruff check src/ tests/ conftest.py — clean
• python -m mypy src/ — 29 errors (was 42), untouched files unchanged
• pytest tests/repositories/ tests/test_database.py tests/test_database_pool.py tests/test_database_write_lock.py tests/test_migrations.py tests/test_migrations_schema_paths.py — 496 passed

🤖 Generated with Claude Code

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