Add scrollback recovery script for the test-pollution incident

[buggerman]

Summary

• Companion to Make ServerStore instance-based so tests can't poison production servers.json #34. The ServerStore-injection PR stopped further damage to servers.json, but it doesn't help users whose real chat history is now stranded under orphan UUID directories in ~/Library/Application Support/Brygga/scrollback/.
• New Scripts/recover-scrollback.sh walks the disk, lists orphan scrollback dirs sorted by recency, and prints exact mv commands the user can copy after re-adding their server. Read-only by design — never moves or deletes anything itself.
• Filters out empty dirs and collapses pure test-fixture noise (_test, alice, __server__ only) into a single summary line so the user's real chat history stays visible.

Changes

• Scripts/recover-scrollback.sh — new file, executable. ~170 lines of bash + one-liner Python embed for JSON parsing (avoids jq dependency since python3 ships with macOS).
  • Section 1 prints active server UUIDs from servers.json.
  • Section 2 prints networks discovered in ~/Library/Logs/Brygga/ (the user's real network names, intact because DiskLogger keys by network not UUID).
  • Section 3 lists orphan scrollback dirs with MOST RECENT / FILES / FIRST 10 CHANNELS, sorted newest-first. Empty dirs and pure-test-fixture orphans are excluded; test pollution is summarized as a count.
  • Section 4 walks the user through the 5-step recovery procedure with concrete commands.

Test plan

• swift build / swift test — N/A, docs/script only (no source code).
• swiftformat --lint . — N/A, no Swift changed.
• Manual:
  • ./Scripts/recover-scrollback.sh runs against my real scrollback directory and surfaces 4 real orphan dirs (Libera sessions) above 143 hidden test-fixture orphans.
  • Output identifies channel filenames correctly even with the space in Application Support (initial bug — find | xargs was word-splitting; fixed with -print0).
  • No write/delete operations performed; verified by inspection.
  • On a machine with no orphans, prints the "None found" branch.

Risk / rollback

• Script is read-only by design — it never invokes mv, rm, or any other mutation. Only prints commands.
• Bundled in Scripts/ alongside build-app.sh. Not built into the app, not run by CI, not invoked at app launch.
• Revert: this single commit. Removing the script has no impact on the running app.

Follow-up (separate PR)

Same injection treatment for ScrollbackStore.shared and ScrollbackIndex.shared so IRCSessionTests stops creating fresh orphan dirs on every swift test run. Today, every test pass adds ~30 new orphans (visible at the top of the recovery script's hidden-summary count). Lower priority than the ServerStore fix because the impact is "more dirs accumulate" not "user data overwritten", but worth fixing for hygiene.