fix: make interrupted indexing retryable and reset cancelled dialogs

[mrsibe]

What does this PR do?

Fixes the remaining Quiz/Anki Cancel reset paths and makes interrupted indexing visible and retryable after restarting the desktop app.

Why?

Cancel buttons bypassed the dialogs' reset handlers, leaving temporary question/card counts, difficulty, and prompts behind when reopening.

The ingestion queue is in memory. Exiting during indexing left persisted documents in pending or processing, displaying an indexing spinner indefinitely without a Retry action.

What changed?

• Route both Cancel buttons through their existing handleOpenChange(false) reset paths.
• After database migrations and before starting ingestion services or watched-folder reconciliation, mark leftover pending/processing documents as failed.
• Persist an interruption explanation and update the timestamp so the existing failed-source UI exposes the error and Retry action.
• Preserve source content, local paths, chunk counts, and completed/previously failed documents.
• Add SQL-backed regression coverage for status recovery, preservation of source data, idempotence, startup ordering, and both Cancel paths.

This is deliberately not a durable queue or automatic resume implementation. Existing retry prerequisites still apply: a source needs saved content or a local copy. A URL interrupted before either is saved may need to be imported again.

How was this tested?

• npm test: 493/493 tests passed.
• npm run build: passed, including the full npm run typecheck gate.
• npm run build:unpack: passed on Linux x64.
• npm run smoke:packaged: passed, including 29 packaged-app checks.
• Targeted ESLint: no errors; two existing no-explicit-any warnings.
• git diff --check: passed.
• The recovery SQL was exercised against an in-memory SQLite database. A manual exit/relaunch during a real indexing job and interactive Cancel/reopen testing were not performed.

Checklist

• I have reviewed my own changes.
• npm run typecheck passes.
• npm run build passes.
• I have tested the affected user workflow.
• I have not included unrelated changes.
• I have updated documentation when necessary. (No separate documentation changes needed.)

Desktop / build changes

• Not applicable
• npm run build:unpack passes.
• npm run smoke:packaged passes.