fix: do not serve user feed from PDS

[hacdias]

This closes #41 by not serving the user's feed directly from their PDS. Please read the issue for the rationale behind this.

On the issue, I also mentioned:

Create some mechanism through which the user profile could be "repaired" if the user notices something missing.

However, I've read through the code and seen that synchronization is already triggered in many places, from the ingester, authentication, and there's also a /sync API (which should maybe be rate limited? 🤔)

Summary by CodeRabbit

• Chores
  • Simplified internal feed handling logic by removing redundant data fetching pathways.

[coderabbitai]

📝 Walkthrough

Walkthrough

This change removes the serveUserFeedFromPDS function and its associated logic from the GetFeed handler, eliminating the parallel data fetching mechanism that previously retrieved user feed data directly from PDS. The sync import, which was only used by the removed function, is also deleted.

Changes

Cohort / File(s)	Summary
PDS Feed Service Removal backend/internal/api/handler.go	Removed the serveUserFeedFromPDS function (154 lines), the conditional branch in GetFeed that invoked it, and the unused sync package import. This eliminates parallel data fetching from PDS for annotations, highlights, and bookmarks.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

🐰 Hop hop, the feed now flows so clear,
No PDS detours, the path is near!
Old sorting woes and pagination pain,
Simplified code runs through our domain. ✨

🚥 Pre-merge checks | ✅ 6

✅ Passed checks (6 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately summarizes the main change: removing the logic that serves the user feed from PDS, which is the primary objective of this PR.
Linked Issues check	✅ Passed	The PR implements solution #2 from issue #41 by removing PDS feed serving, addressing both wrong ordering and missing items problems identified in the linked issue.
Out of Scope Changes check	✅ Passed	All changes are directly scoped to the removal of serveUserFeedFromPDS functionality and its related import, with no extraneous modifications.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Merge Conflict Detection	✅ Passed	✅ No merge conflicts detected when merging into main

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✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

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No actionable comments were generated in the recent review. 🎉

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