Fix file content search reset per worktree

[AmethystLiang]

Problem

• File content search state was global, so switching or deleting worktrees could leave the sidebar showing stale query text, filters, collapse state, and results from a different worktree.
• The reset path around worktree removal was not covered by store cascade tests, which made this regression easy to reintroduce.

Solution

• Scope file search state by worktree in the editor store and update the search sidebar to read and write the active worktree's state.
• Drop cached file-search state when a worktree is removed, with an inline why-comment documenting the cleanup requirement.
• Add cascade tests for search-state cleanup/preservation and extract the include/exclude filter UI into a small component to keep the sidebar implementation within repo lint limits.