feat(ui): context- and state-aware bottom keybinding strip (#27)

Per ADR-0051 (closing issue #27): the bottom status line is now a
keystrokes-only, state-selected strip. A pure status_bar_bindings()
picks the binding set by priority (first match wins):

  sidebar focus   → Ctrl-O next pane · ↑↓/PgUp/PgDn scroll · Esc input
  completion live → Tab/Shift-Tab cycle · Esc cancel · Enter run
  history nav     → ↑↓ browse · Esc clear · Enter run
  editing         → Esc clear · Ctrl-A/E home/end · Ctrl-W del word · Enter run
  default (empty) → Ctrl-O sidebar · Tab complete · ↑ history · Enter run

The editing state surfaces the #29 readline keys (ADR-0049's deferred
advertisement). Typed-command words (mode advanced/simple, the ':'
one-shot) and Ctrl-C quit leave the strip; simple mode's empty-input
hint gains a '`mode advanced` for SQL' pointer (advanced mode shows
none — a switcher knows the way back, and help covers it).

Mechanism: status_bar_bindings + a thin renderer (unit-testable);
App::is_browsing_history() exposes the private history_cursor; the mode
pointer lives in resolve_hint_lines. Catalog: 12 new shortcut labels +
panel.hint_mode_advanced (en-US.yaml + keys.rs, validator 1:1), 5 dead
strip strings removed.

Forks user-chosen: editing state shows #29 keys; quit omitted; no
width-drop machinery (longest strip ~65 cols fits; a width-budget test
keeps it lean). Modal-aware strip is OOS (pre-existing). Tests: 9
Tier-1 unit (per-state key sets, width budget, mode pointer), 1 Tier-3
rewritten, 15 full-panel snapshots re-accepted (reviewed). 2467 pass /
0 fail / 0 skip, clippy clean.

src/friendly/keys.rs

@@ -446,6 +446,7 @@ pub const KEYS_AND_PLACEHOLDERS: &[(&str, &[&str])] = &[
     ("undo.redo_failed", &["error"]),
     // ---- Status bar + panels ----
     ("panel.hint_empty", &[]),
+    ("panel.hint_mode_advanced", &[]),
     ("panel.hint_title", &[]),
     ("panel.output_title", &[]),
     ("panel.relationships_empty", &[]),
@@ -462,18 +463,25 @@ pub const KEYS_AND_PLACEHOLDERS: &[(&str, &[&str])] = &[
     ("save.title_as", &[]),
     ("save.title_save", &[]),
     // ---- Shortcut hint labels ----
-    ("shortcut.advanced_once", &[]),
     ("shortcut.back_to_list", &[]),
+    ("shortcut.browse", &[]),
     ("shortcut.browse_path", &[]),
     ("shortcut.cancel", &[]),
-    ("shortcut.cancel_one_shot", &[]),
+    ("shortcut.clear", &[]),
+    ("shortcut.complete", &[]),
     ("shortcut.confirm", &[]),
+    ("shortcut.cycle", &[]),
+    ("shortcut.del_word", &[]),
+    ("shortcut.history", &[]),
+    ("shortcut.home_end", &[]),
     ("shortcut.load", &[]),
+    ("shortcut.nav", &[]),
+    ("shortcut.next_pane", &[]),
     ("shortcut.no", &[]),
-    ("shortcut.quit", &[]),
+    ("shortcut.run", &[]),
+    ("shortcut.scroll", &[]),
     ("shortcut.select", &[]),
-    ("shortcut.submit", &[]),
-    ("shortcut.switch", &[]),
+    ("shortcut.to_input", &[]),
     ("shortcut.yes", &[]),
     // ---- mode / messages banners ----
     ("messages.set_short", &[]),