build: speed up debug compile loop

- Drop libsqlite3-sys 'bundled' on Linux/macOS so the SQLite C source
  isn't recompiled every clean build; Windows keeps 'bundled' via a
  cfg(windows) target override.
- Switch opentelemetry-otlp from grpc-tonic to http-proto + reqwest-client.
  Removes the tonic + h2 + hyper-h2 stack from the build graph; reqwest
  was already a dependency. Updates otel.rs to call .with_http().
- Add [profile.dev] debug = "line-tables-only" to shrink linker work
  while keeping panics/backtraces useful.
- Add .cargo/config.toml selecting mold via gcc on x86_64-linux-gnu.
  Requires `apt install mold`. Other platforms use the default linker.
- cargo update: lockfile-only refresh of all minor/patch bumps within
  existing version constraints.

Cold debug build: ~1m 37s; touch-one-file rebuild: ~5s on Linux.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.cargo/config.toml

@@ -0,0 +1,3 @@
+[target.x86_64-unknown-linux-gnu]
+linker = "/usr/bin/gcc"
+rustflags = ["-C", "link-arg=-fuse-ld=mold"]