Add context-aware items to the command palette

When opened with Ctrl-K, the palette now prepends entries for whatever
is currently focused:

- Focused scratchpad: Delete / Rename (inline form) / Edit (fire-and-
  forget zed launch with stdio detached so the TUI is not suspended).
- Focused agent: Rename (inline form) / Close.
- Focused process: Rename / Delete (drops the entry; SIGKILL if alive)
  / Stop (SIGTERM, keep entry) / Restart (same argv).

The rename UX is a single-field inline form that mirrors the existing
spawn-process form, so the modal-input contract is unchanged.
scratchpad.Store grows Delete / Rename / Path so the palette can act
on a pad file by name. focusedPad is plumbed onto uiState ahead of the
scratchpad-focus UI work; until that lands it stays empty and the
scratchpad-context entries simply never surface.

Tested with palette_context_test.go and a new rename_process_via_palette
harness scenario.

CHANGELOG.md

@@ -16,6 +16,14 @@ loosely follows [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
   re-typing. `close_process` (and the palette's close action) drops
   the entry, and rename / "relaunch on exit" toggles are mirrored as
   they happen. Agents and terminals stay ephemeral by design.
+- The command palette (Ctrl-K) now surfaces context-aware actions at
+  the top of the list, based on what's currently focused:
+  - Scratchpad in focus: `Delete`, `Rename` (inline form), and `Edit`
+    (fire-and-forget launch of `zed` against the pad file).
+  - Agent in focus: `Rename agent` (inline form) and `Close agent`.
+  - Process in focus: `Rename process`, `Delete process` (drops the
+    entry; SIGKILLs if alive), `Stop process` (SIGTERM, keep entry),
+    and `Restart process` (same argv).
 - `patterm --version` prints the build version, git commit, and build
   date (e.g. `patterm v0.0.1 (commit abc1234, built 2026-05-14)`). The
   version string is injected by the build (`make patterm` derives it