fix: support source re-ingestion and removal

[Aaqibhafeezkhan]

Closes #18

[francescobianco]

Thank you @Aaqibhafeezkhan, this is a substantial contribution and it closes one of the most important gaps in gknowledge.

Until now, ingestion was a one-way street: if a document was updated, ingested with the wrong model, or simply did not belong in the project, the only fix was to start a new knowledge base. With this PR the knowledge base becomes something you can actually maintain over time, which is the whole point of the "evolving knowledge base" idea.

What makes it solid:

• Provenance-aware cleanup. _detach_source deletes only the pages that the source alone supported, while pages shared with other sources are kept and just lose the [[source]] link. A shared concept page never disappears because one of its sources was removed.
• No stale state left behind. Jobs, review items, mentions.json entries, the index, the overview and the log are all updated, so the wiki, the database and the cache stay consistent.
• Safe by design. _managed_path refuses paths outside sources/ and knowledge/, both actions are blocked while an ingestion is running, and Remove asks for confirmation with a destructive-styled dialog.
• Tests for both flows, including the tricky case of a page shared between two sources.

Great work, and thank you again!

[francescobianco]

@Aaqibhafeezkhan since you now know the source→page lifecycle better than anyone, here are the open issues that build directly on this PR, in case you want to keep going:

• Wiki lint: orphans, broken links and duplicate titles #14 Wiki lint (orphans, broken links, duplicate titles) and its older twin Add a lint command for orphan pages and broken [[links]] #2: _detach_source already removes [[source]] links, and the same logic could report pages with no inbound links and [[links]] pointing to deleted pages. It's a natural next step and also a safety net for this PR. These two could be merged into a single PR that closes both.
• Watch sources/ for changes with Gio.FileMonitor #3 Watch sources/ with Gio.FileMonitor: reingest_source is exactly what a modified file should trigger. A monitor that marks the source as changed and offers Re-ingest would close the loop.
• Ingest several sources in parallel #15 Ingest several sources in parallel: re-ingest and remove are currently guarded by is_running(). If you touch Ingest several sources in parallel #15, please keep that guard (or a per-source lock) so nobody can remove a source while it's being ingested.

None of this is required for merging #30. They're just the places where your work pays off most. And of course, the invitation to join https://github.com/openapi/contributors stands 🙂

[Aaqibhafeezkhan]

@Aaqibhafeezkhan since you now know the source→page lifecycle better than anyone, here are the open issues that build directly on this PR, in case you want to keep going:

• Wiki lint: orphans, broken links and duplicate titles #14 Wiki lint (orphans, broken links, duplicate titles) and its older twin Add a lint command for orphan pages and broken [[links]] #2: _detach_source already removes [[source]] links, and the same logic could report pages with no inbound links and [[links]] pointing to deleted pages. It's a natural next step and also a safety net for this PR. These two could be merged into a single PR that closes both.
• Watch sources/ for changes with Gio.FileMonitor #3 Watch sources/ with Gio.FileMonitor: reingest_source is exactly what a modified file should trigger. A monitor that marks the source as changed and offers Re-ingest would close the loop.
• Ingest several sources in parallel #15 Ingest several sources in parallel: re-ingest and remove are currently guarded by is_running(). If you touch Ingest several sources in parallel #15, please keep that guard (or a per-source lock) so nobody can remove a source while it's being ingested.

None of this is required for merging #30. They're just the places where your work pays off most. And of course, the invitation to join https://github.com/openapi/contributors stands 🙂

Thanks @francescobianco Will check them out :)