Add c to copy the selected path, split key bar into groups

c copies the absolute directory of the selected submodule via OSC 52.
Keys are grouped into navigation (footer left), global (footer right)
and submodule (detail pane palette, footer if the pane can't show it).
Adds a key reference table to the UX guide.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

docs/decisions.md

@@ -200,3 +200,21 @@ package so versions stay clean.
 corrupt or partial downloads, not a compromised registry (no signatures).
 The update check is a deliberate, outside-the-provider network use: only
 on `update` and a once-a-day background check that can be disabled.
+
+## Copy path with `c` via OSC 52
+
+`c` copies the selected submodule's absolute directory (optional
+`submodule.Locator`; the relative path as fallback). The absolute path is
+what a shell needs (`cd <paste>`). OSC 52 instead of a clipboard tool
+(`xclip`, `pbcopy`): no external dependency and it works over SSH. The cost:
+terminals that block OSC 52 copy nothing silently; the footer still says
+`copied`, since the application can't know.
+
+## Key groups: global, navigation, submodule
+
+Keys that act on the selected submodule (copy path, later checkout, bump) are
+shown in a palette in the detail pane, next to what they act on; global keys
+(`?`, `q`) sit right in the footer. Where the pane can't show the palette
+(hidden below 90 columns, or under 12 lines) the footer shows these keys
+instead, so small terminals need no extra UI (no overlay or action menu).
+Keys never depend on what is visible.