[Horuse]

What does this PR do?

Makes crash reports useful when there is no stack

• Session log on disk. The log is mirrored to session.log in the app log dir and capped at 4 MB. On start the old file becomes previous-session.log; after an unclean exit its last 300 lines go into the crash report.
• Main-thread hang detection. A watchdog thread probes the main thread with run_on_main_thread. After 5 s without an answer it writes hang.json, naming the IPC command the main thread is stuck in. If the app is then killed, the next launch shows a hang ("Not responding") report instead of "did not shut down cleanly".
• Webview errors. onerror and unhandledrejection are written to the same log through log_frontend.
• Redaction. Before the log is attached, the home directory becomes ~ and IP addresses become <ip>, since reports end up in public issues.
• Error modal. Shows a "Session log" block. "Copy details" includes the full log; the GitHub link includes the last 60 lines (URL length).
• Debug panel. Adds "Main thread hang (20 s)".

Why is this the right approach?

• Logging: tracing-appender's non-blocking writer in non-lossy mode. Its rolling appender rotates only by time, and we need one file per session, so rotation stays ours.
• Hangs: no crate or Sentry Rust SDK feature detects hangs, so the watchdog is ours. The marker is written synchronously, so it survives a kill.
• Redaction: regex was already in the tree through tracing-subscriber. Candidates are confirmed with std's Ipv4Addr/Ipv6Addr parsers.
• Out of scope: minidumps (crash-handler + minidumper, including dumps on hang) and Sentry come later, in separate PRs.

Checklist

• Diff is limited to the change, no unrelated edits
• bun run check passes
• cargo check --manifest-path src-tauri/Cargo.toml passes
• bun run format leaves the tree clean
• Generated TS types are committed with the Rust change (none)
• New dependencies explained above (tracing-appender, regex)
• No changes to the RT audio path; nothing logs from audio callbacks

Platform coverage

• Developed on: macOS
• Tested on: macOS (dev build)
• What I did to test: "Main thread hang" from the debug panel, then a kill, then a relaunch. The modal showed a hang report naming debug_hang, with the previous session log. Recovery after a hang is logged. Unit tests cover redaction.
• Not tested: Windows, Linux

No per-OS files. The watchdog relies on run_on_main_thread, and the log dir comes from Tauri's app_log_dir on every platform.