feat: clean-room rewrite — replace ported modules with original implementations

Every Rust module under src/ that previously contained upstream-derivative
code has been replaced by a from-scratch implementation:

  diag/    log + simplelog file appender (was: diagnose.rs)
  os/      color, dpi, registry, string, theme (was: theme.rs, native_interop.rs)
  net/     WinHTTP-based HTTP client (was: ureq + native-tls)
  i18n/    TOML-embedded locale tables (was: localization/*.rs)
  usage/   trait UsageProvider + ClaudeProvider + ChatGptProvider + refresh
           orchestrator + registry (was: poller.rs, models.rs)
  creds/   trait CredentialSource + local/WSL/Codex impls (was: poller.rs)
  tray/    stateless tray manager + tiny-skia anti-aliased badge renderer
           (was: tray_icon.rs)
  update/  release fetch + inline cmd /c handoff installer
           (was: updater.rs's helper-exe pattern)

Application files (app.rs, bubble.rs, panel.rs, settings.rs) migrated to
the new modules. main.rs declares only the new modules.

NOTICE deleted; LICENSE is plain Apache-2.0; README updated to credit
inspiration rather than claim derivation. Cargo.toml drops ureq + native-tls
+ winres in favour of log + simplelog + thiserror + toml + tiny-skia +
embed-resource. Build script swapped to embed-resource via res/icon.rc.

External contracts preserved unchanged: Anthropic + ChatGPT endpoints and
headers, ~/.claude/.credentials.json + Codex auth.json paths, WSL bridging
via wsl.exe, CLI-driven token refresh, GitHub Releases JSON shape, Windows
registry path for startup, single-instance mutex name.

Phase docs: plans/260516-0707-cleanroom-rewrite/.

src/bubble.rs

@@ -18,9 +18,11 @@ use windows::Win32::UI::HiDpi::*;
 use windows::Win32::UI::Shell::ExtractIconExW;
 use windows::Win32::UI::WindowsAndMessaging::*;
 
-use crate::diagnose;
-use crate::native_interop::{wide_str, Color, TIMER_FULLSCREEN_CHECK};
-use crate::tray_icon::TrayIconKind;
+use crate::os::{to_utf16_nul as wide_str, Rgb as Color};
+
+const TIMER_FULLSCREEN_CHECK: usize = 5;
+use crate::usage::ProviderId;
+type TrayIconKind = ProviderId;
 
 // ---------- Public types & API ----------
 
@@ -58,7 +60,7 @@ pub fn register_class() {
             ..Default::default()
         };
         if RegisterClassExW(&wc) == 0 {
-            diagnose::log("bubble RegisterClassExW returned 0");
+            log::error!("bubble RegisterClassExW returned 0");
         }
     });
 }
@@ -98,7 +100,7 @@ pub fn create(config: BubbleConfig) -> HWND {
     };
 
     if hwnd == HWND::default() {
-        diagnose::log("bubble CreateWindowExW failed");
+        log::error!("bubble CreateWindowExW failed");
         return hwnd;
     }
 
@@ -807,8 +809,8 @@ fn default_position(size_px: i32, model: TrayIconKind) -> (i32, i32) {
         };
         let gap = 24;
         let stagger = match model {
-            TrayIconKind::Claude => 0,
-            TrayIconKind::Codex => size_px + gap,
+            ProviderId::Claude => 0,
+            ProviderId::ChatGpt => size_px + gap,
         };
         let x = wa.right - size_px - gap;
         let y = wa.bottom - size_px - gap - stagger;