feat: redesign bubble as two-bar rounded rect, finish port wiring

Bubble shape changes from circle to rounded rectangle showing two stacked
horizontal bars — top: session (5h), bottom: weekly (7d) — each followed
by a right-aligned "X% · Yh Zm" string (percent + countdown).

Bubble surface:
- BubbleConfig/BubbleState carry session+weekly percents and texts (mirrors
  PanelData); update_percentage renamed to update_data
- Aspect ratio fixed at 3:1; size_logical is interpreted as width with
  height derived. Clamp is 120..360 (was 32..128 square)
- Hit-testing uses a rounded-rect predicate (point_in_rounded_rect) shared
  with the alpha mask so paint and click area can't drift
- New rgb_to_dib helper for direct DIB writes — BI_RGB 32bpp stores B,G,R,X
  in memory which is the opposite of COLORREF. The previous code wrote
  COLORREF-packed u32 straight into DIB pixels; invisible while every color
  was gray, but the new orange/red bar fills would have rendered blue
- bar_h capped at h/4 (range 6..18) so the text font derived from it stays
  small enough that "100% · 23h" fits in right_text_w (= 6×bar_h, min 56);
  the first iteration had a 19-px font in a 60-px column and ellipsized
  away the countdown
- Initial session_text/weekly_text seeded with "…" so the bubble has
  visible feedback during the first poll instead of two empty grey tracks

Compile + cleanup needed to make the port build at all:
- Color::from_hex added back as an infallible wrapper around parse_hex
  (15 call sites in bubble.rs/panel.rs assumed the old infallible API)
- Color::to_colorref → into_colorref at 5 call sites
- GetModuleFileNameW added to the LibraryLoader import in bubble.rs
- usage::Error gains Creds(#[from] creds::Error) so `?` works in the
  Anthropic and ChatGPT providers
- FlattenBoxed::flatten renamed to flatten_box — the std Option::flatten
  was shadowing it and yielding Option<Box<T>> instead of Option<T>
- PanelState marked unsafe Send (HWND has *mut c_void; state is only
  touched from the UI thread, Mutex is for OnceLock satisfaction)
- Crate-level #![allow(dead_code)] for in-progress port API surface
  (creds, usage, update, os::dpi); unused pub-use re-exports removed

App wiring:
- propagate_to_ui now feeds both windows + their formatted texts into
  update_data (was a single percent)

src/panel.rs

@@ -41,6 +41,11 @@ struct PanelState {
     data: PanelData,
 }
 
+// HWND wraps `*mut c_void` which is `!Send`, but the panel state is only ever
+// accessed from the UI thread — the Mutex exists to satisfy the `OnceLock`
+// static contract, not because of real cross-thread sharing.
+unsafe impl Send for PanelState {}
+
 fn state() -> &'static Mutex<Option<PanelState>> {
     static S: OnceLock<Mutex<Option<PanelState>>> = OnceLock::new();
     S.get_or_init(|| Mutex::new(None))
@@ -267,7 +272,7 @@ fn paint(hwnd: HWND, hdc: HDC) {
     let accent = bar_color_for(data.session_pct.max(data.weekly_pct), data.is_dark);
 
     unsafe {
-        let bg_brush = CreateSolidBrush(COLORREF(bg.to_colorref()));
+        let bg_brush = CreateSolidBrush(COLORREF(bg.into_colorref()));
         FillRect(hdc, &rc, bg_brush);
         let _ = DeleteObject(bg_brush);
 
@@ -362,7 +367,7 @@ fn draw_row(
     );
 
     unsafe {
-        let track_brush = CreateSolidBrush(COLORREF(track.to_colorref()));
+        let track_brush = CreateSolidBrush(COLORREF(track.into_colorref()));
         let bar_rect = RECT {
             left: bar_x,
             top: row_y,
@@ -374,7 +379,7 @@ fn draw_row(
 
         let fill_w = ((pct.clamp(0.0, 100.0) / 100.0) * bar_w as f64).round() as i32;
         if fill_w > 0 {
-            let accent_brush = CreateSolidBrush(COLORREF(accent.to_colorref()));
+            let accent_brush = CreateSolidBrush(COLORREF(accent.into_colorref()));
             let fill_rect = RECT {
                 left: bar_x,
                 top: row_y,
@@ -439,7 +444,7 @@ fn draw_text(
             PCWSTR::from_raw(font_name.as_ptr()),
         );
         let old_font = SelectObject(hdc, font);
-        SetTextColor(hdc, COLORREF(color.to_colorref()));
+        SetTextColor(hdc, COLORREF(color.into_colorref()));
         SetBkMode(hdc, TRANSPARENT);
         let mut rect = RECT {
             left: x,