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code has been replaced by a from-scratch implementation: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/.

Cargo.toml

@@ -7,20 +7,20 @@ description = "Floating bubble showing Claude Code and Codex usage on Windows"
 homepage = "https://github.com/tiennm99/claude-code-usage-bubble"
 repository = "https://github.com/tiennm99/claude-code-usage-bubble"
 
-[package.metadata.winres]
-ProductName = "Claude Code Usage Bubble"
-FileDescription = "Claude Code Usage Bubble"
-OriginalFilename = "claude-code-usage-bubble.exe"
-InternalName = "ClaudeCodeUsageBubble"
-LegalCopyright = "Copyright (C) 2026"
-Comments = "Floating bubble showing Claude Code and Codex usage on Windows"
-
 [dependencies]
+# `ureq` + `native-tls` are kept while the legacy `poller.rs` and `updater.rs`
+# modules survive. Phase 4 deletes `poller.rs` and Phase 6 deletes `updater.rs`,
+# at which point these two deps go away in favour of `net::winhttp`.
 ureq = { version = "2", default-features = false, features = ["native-tls", "json", "proxy-from-env"] }
 native-tls = "0.2"
 serde = { version = "1", features = ["derive"] }
 serde_json = "1"
 dirs = "6"
+log = "0.4"
+simplelog = "0.12"
+thiserror = "2"
+toml = "0.8"
+tiny-skia = "0.11"
 
 [dependencies.windows]
 version = "0.58"
@@ -36,10 +36,11 @@ features = [
     "Win32_Security",
     "Win32_UI_HiDpi",
     "Win32_UI_Input_KeyboardAndMouse",
+    "Win32_Networking_WinHttp",
 ]
 
 [build-dependencies]
-winres = "0.1"
+embed-resource = "3"
 
 [profile.release]
 opt-level = "z"