feat(adapters): add GoAdapter driving dlv dap

[niradler]

Summary

Second PR in the multi-language stack. Stacks on top of #2 (Adapter ABC refactor) — merge that first; once merged, this PR's base will be main.

GoAdapter implements the Adapter contract for Go programs:

• Adapter spawn — dlv dap --listen=127.0.0.1:<port>, with a clear "delve not installed" error pointing at the go install command when dlv isn't on PATH (no cryptic ENOENT).
• Launch payload — mode: "debug" so delve compiles + runs in one step from a .go file or package directory.
• spawn_listen_mode for IDE attach (VS Code Go extension dap-mode).
• parse_traceback understands both panic: and fatal error: dumps, including extended runtime frames with +0xN fp=0x... sp=0x... pc=0x... annotations. Frames stored oldest-first so the shared deepest_user_frame heuristic lands on the panic site. runtime.* / sync.* / reflect.* / internal/* frames are marked is_user_code=False.
• resolve_launch_target peels go run [-flags] <main.go> args... into (main.go, args) for dbga diagnose. go test is out of scope (would need mode: "test").

CLI

dbga session start --break-at main.go:12 -- main.go
dbga diagnose --timeout 30 -- go run main.go
dbga localize --lang go --file panic.txt

Language is auto-detected from the script extension; --lang go forces it.

Test plan

• 14 new unit tests (tests/unit/test_go_adapter.py) — registry, detection, listen-mode flag, launch-payload shape, go run peeling, panic + fatal-error parsing, missing-dlv error path.
• 1 new integration test (tests/integration/test_go_session.py) — drives real dlv dap end-to-end (initialize / launch / stopOnEntry / continue / terminated). Auto-skips when dlv or go isn't on PATH.
• uv run pytest -v — 128 passed (61 unit + 14 Go unit + 1 misc, 8 integration, 45 e2e), driven against real delve 1.22+ on Windows.
• uv run ruff check . clean
• uv run ruff format --check . clean
• uv run mypy src clean (29 files)
• __debug_bin* + *.test added to .gitignore (dlv dap leaves the compiled binary in cwd).

Out of scope (deferred)

• go test ./... debugging (needs DAP mode: "test" + --test.run plumbing).
• dbga instrument probe templates for Go (fmt.Println defaults).

Stack

• refactor(adapters): introduce language Adapter ABC; lift Python-specific code behind it #2 — refactor: Adapter ABC (merge first).
• This PR — GoAdapter.
• Next — NodeAdapter via vscode-js-debug.

[niradler]

Superseded by #5, which consolidates the refactor + Go + Node work into a single PR against main (with post-review fixes applied). Closing in favor of #5.