feat(editor): add v0.5 file palette (Cmd-P) with fuzzy match

Cmd-P opens a modal transient palette over the writing column: a bare
fuzzy-search input, the ranked file list, and the selected row in reverse
video. A pure host-testable fuzzy_score (subsequence + word-boundary and
consecutive-run bonuses) ranks results; an in-core MRU floats recently
opened files first and is shared with :e (both route through open_path).
The host feeds the file list once at boot (enumerate_files over /sd/repo
and /sd/local). Ctrl-n/Ctrl-p navigate the list; Enter opens via the same
park/evict path as :e; Esc closes.

Ctrl-n/Ctrl-p also become down/up line motions in Normal and View (vim
CTRL-N/CTRL-P, count-aware), which is why the palette opener is Cmd-P
alone. No `>` prefix on the file input — `>` is reserved for the command
palette (slice 4).

112 editor + 28 keymap tests; the no-git firmware binary builds clean.

CONTEXT.md

@@ -48,7 +48,7 @@ _Avoid_: tab, window, document (a buffer is not a UI chrome element); "the file"
 when you mean the in-memory copy rather than the bytes on the card.
 
 **Open**:
-Bringing a **File** into the **active buffer**, via `Ctrl-P` (the file palette)
+Bringing a **File** into the **active buffer**, via `Cmd-P` (the file palette)
 or `:e`. Scope is read from where the file lives (`/sd/repo` → **Tracked**,
 `/sd/local` → **Local**), never chosen at open time.
 _Avoid_: load (implementation talk for the disk read behind an Open).