feat(cli): show forge binary/runtime version on the startup banner (#335)

[initializ-mk]

Closes #335.

Problem

The startup banner printed the agent's forge.yaml version but never the forge binary running it, so it was hard to tell which runtime (v0.17.0, a vnext/dev build, or a locally-built binary) was executing a deployed agent. The build version already existed (-X main.version / -X main.commit via the Makefile + goreleaser) and was threaded to the runner as RuntimeVersion — it just wasn't shown; commit was baked only into the --version template.

Change

  Agent:      my-agent (v1.2.0)       # agent's forge.yaml version
  Forge:      v0.17.0 (commit: 51df9a4)   # ← NEW: the forge binary/runtime
  Framework:  ...

• root.go — store commit in appCommit (was discarded after building the version template).
• run.go — pass RuntimeCommit alongside the existing RuntimeVersion: appVersion.
• runner.go — add RunnerConfig.RuntimeCommit + a Forge: banner line via forgeVersionString().

Degradation: a dev build / no baked commit shows just the version (dev, v0.17.0); the none sentinel and empty commit suppress the (commit: …) suffix. forge --version output is unchanged.

Verification

• forgeVersionString() covered by a table test (release+commit, release no-commit, empty commit, dev defaults, empty version → dev, empty version + real commit).
• Built with -ldflags "-X main.version=v0.17.0 -X main.commit=abc1234" → forge --version → forge v0.17.0 (commit: abc1234) (unchanged).
• Banner line is a single Fprintf inserted right after the existing Agent: line; gofmt + golangci-lint clean, go build ./... green.