fix(debug-log): prevent ingest route startup panic

[limityan]

Summary

• update the debug log ingest route to axum's {session_id} path parameter syntax
• add a regression test that starts the ingest server and catches router-construction panics

Root cause

Axum rejects route segments starting with :. The debug ingest server still registered /ingest/:session_id, so debug-mode startup could panic while building the router before the app finished opening.

Validation

• pnpm run fmt:rs
• cargo test -p bitfun-core infrastructure::debug_log::http_server::tests::starts_with_session_id_ingest_route -- --nocapture
• cargo check -p bitfun-core
• git diff --staged --check