add quick-open fuzzy file finder (Ctrl/Cmd+P)

A file picker overlay over the whole workspace, distinct from the
command palette. QuickOpenController holds the file list + a
subsequence fuzzy filter; the overlay loads the list via files.walk on
open, shows RecentFilesService entries on an empty query, and opens the
selection through a shared openWorkspaceFile helper (.md → markdown
reader bus, else editor.open) that the files panel now also routes
through, so recents stay in sync from every open site.

Bound to ctrl+p / meta+p with `when: !palette.open` so it never
collides with the palette's ctrl+p navigation; in-overlay arrows/enter/
escape reuse the palette's keymap-driven model via quickOpen.* intents.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

CHANGELOG.md

@@ -18,6 +18,10 @@ heading, and (b) bumping `pubspec.yaml` `version:` in the same commit.
 
 ### Added
 
+- Quick-open file finder (Ctrl/Cmd+P): a fuzzy file picker overlay over the
+  whole workspace, separate from the command palette. Empty query lists recent
+  files; Enter opens `.md` in the markdown reader and other files in the editor.
+  (T-51)
 - Workspace ignore now follows the `ignore_files:` list in `.pql/config.yaml`
   (ordered, later-wins, per D-4) instead of a hardcoded `.gitignore` +
   `.clideignore` pair — the single ignore knob clide owns. (T-52)