redbear-power: surface tab keys in --help and Controls panel

The tab keys (1-9 jump directly, T cycles next) were
always wired in main.rs but not documented anywhere
visible. Operators could not discover how to switch
between the 9 data tabs (Per-CPU / System / Info /
Motherboard / Battery / Sensors / Network / Storage
/ Process) without reading the source.

Two surfaces now surface the tab keys as the FIRST
entries, ahead of governor / P-state / throttle
controls:

1. Controls panel (visible at the bottom of every
   TUI frame): adds a 'Tabs:' line listing the 9
   direct-jump keys with abbreviated tab names, plus
   a [T] cycle line. Implemented in
   render_controls().

2. --help output (HELP_TEXT constant, shown via
   'redbear-power --help' and the in-TUI [?] help
   overlay): adds a TABS: section at the top of the
   INTERACTIVE CONTROLS block, listing all 9 tabs in
   3-row grid + the [T] cycle key.

The keys themselves are unchanged: '1'-'9' for
direct tab jump, 'T' for cycle. No new keybindings
or behaviors added.

Discovered during interactive smoke-testing on the
Linux host: the binary worked perfectly but tab
navigation was a discoverability hole. Fix-only,
no semantic change.

186/186 tests still pass (the controls panel
render is covered by the existing snapshot tests).

local/recipes/system/redbear-power/source/src/render.rs

@@ -1530,6 +1530,16 @@ pub fn render_controls<'a>(app: &'a App, focused: bool) -> Paragraph<'a> {
     let mut lines = vec![
         Line::from("Controls".set_style(theme::LABEL_BOLD)),
         Line::from(""),
+        Line::from(vec![
+            "  Tabs: ".yellow(),
+            "[1]PerCPU [2]Sys [3]Info [4]MB [5]Batt [6]Sens \
+             [7]Net [8]Stor [9]Proc".into(),
+        ]),
+        Line::from(vec![
+            "         ".into(),
+            "[T] cycle (next tab)".into(),
+        ]),
+        Line::from(""),
         Line::from(vec!["  [g] ".yellow(), "cycle governor".into()]),
         Line::from(vec!["  [p] ".yellow(), "P-state -1 (slower, cooler)".into()]),
         Line::from(vec!["  [P] ".yellow(), "P-state +1 (faster, hotter)".into()]),
@@ -1658,6 +1668,13 @@ TOML CONFIG:
         auto_stop_temp_c      int or null (default 95)
 
 INTERACTIVE CONTROLS:
+
+TABS:
+    [1] Per-CPU         [2] System         [3] Info
+    [4] Motherboard     [5] Battery        [6] Sensors
+    [7] Network         [8] Storage        [9] Process
+    [T] cycle to next tab
+
     [g]    cycle governor (Performance / Ondemand / Powersave)
     [p/P]  step selected CPU P-state down / up
     [m/M]  force selected CPU to min / max P-state