feat(buildinfo): fall back to debug.BuildInfo when ldflags unset

[aksOps]

Summary

`go install github.com/randomcodespace/codeiq/go/cmd/codeiq@v0.3.0` produces a working binary, but it reports `dev / unknown / unknown` for `codeiq --version` because the `-ldflags -X buildinfo.X=…` path only runs under goreleaser. Same story for local `go build` from a git checkout.

Fix

Add an `init()` hydrate step in `internal/buildinfo` that reads `runtime/debug.BuildInfo` and fills any var still at its default:

Source	Target
`Main.Version` (skips `(devel)` sentinel)	`Version`
`Settings[vcs.revision]` (7-char short hash)	`Commit`
`Settings[vcs.time]`	`Date`
`Settings[vcs.modified]` (only `false → true`, never demotes)	`Dirty`

Resolution priority (per var):

1. `-ldflags -X` (release builds via goreleaser) — wins
2. `runtime/debug.BuildInfo` — `go install …@` or local `go build`
3. Defaults (`dev` / `unknown`) — last resort, e.g. cross-compiled stripped binaries with `-buildvcs=false`

No release-workflow change needed — goreleaser still wins because it sets the vars at link time before `init()` reads them.

Tested locally

```

plain go build (worktree)

$ go build . && ./codeiq --version
codeiq dev
commit: e5fd3fe (dirty)
built: 2026-05-14T01:37:03Z

go install (also locally — full @ path needs this PR merged + a re-tag first)

$ GOBIN=/tmp/gobin go install ./cmd/codeiq && /tmp/gobin/codeiq --version
codeiq dev
commit: e5fd3fe (dirty)
built: 2026-05-14T01:37:03Z

release-style ldflags

$ go build -ldflags "-X buildinfo.Version=v0.3.0 -X buildinfo.Commit=abc1234 -X buildinfo.Date=2026-05-14T00:00:00Z" .
$ ./codeiq --version
codeiq v0.3.0
commit: abc1234 (dirty)
built: 2026-05-14T00:00:00Z
```

After this lands, `go install github.com/randomcodespace/codeiq/go/cmd/codeiq@v0.3.1` (or any future tag) will produce a binary that reports the tagged version + the source commit, with no branch push required at tag-time — the toolchain handles it.

Tests

• 6 buildinfo tests pass (was 5). The old `TestDefaultsWithoutLdflags` was brittle once `init()` ran; replaced with:
  • `TestBuildInfoVarsWellFormed` — vars are non-empty strings; Dirty parses as bool
  • `TestHydratePreservesLdflags` — pins the priority contract via the sync.Once guard
• Full suite: 884 passed.

🤖 Generated with Claude Code