chore: prep v0.6.0 changelog and gitignore Claude Code state

[ojongerius]

Summary

Prep PR for the v0.6.0 release. Lands the CHANGELOG entry and an unrelated-but-blocking .gitignore patch so scripts/release.sh can run cleanly afterward.

Why this is a separate PR

scripts/release.sh requires (a) clean working tree and (b) local main not ahead of origin. With branch protection on main, neither prep commits nor the release commit itself can be pushed directly. Same pattern PR #117 used for v0.5.0: land CHANGELOG additions in a regular PR, then run the release script on a clean main.

What's in here

• .gitignore — ignore three Claude Code local-session paths (settings.local.json, scheduled_tasks.lock, worktrees/). Project-level .claude/settings.json and .claude/hooks/ remain tracked.
• CHANGELOG.md — populate [Unreleased] with the changes from fix(tools): add timestamp/chain filters and newest-first ordering to ar_query_receipts #119:
  • Breaking: ar_query_receipts defaults to current session's chain (use all_chains: true to opt out)
  • Fixed: timestamp_after no longer dropped, newest-first ordering, limit clamping
  • Added: chain_id/timestamp_after/timestamp_before/all_chains filters; chain_id in result objects; polling guidance in tool description
  • Known limitations: links to ReceiptStore.query: support DESC ordering and remove silent default-limit cap ar#300 (SDK cap), ar_query_receipts polling can drop receipts during same-millisecond bursts #121 (same-ms burst), ar_query_receipts: timestamp_after exclusive filter is byte-equality, not instant-equality #122 (instant equality)

No code changes.

Next step

After this merges, run scripts/release.sh minor on a fresh main checkout to produce the actual v0.6.0 release PR.

Test plan

• CI passes (no source code touched, but lefthook/conventional-commit checks should still pass)