fix(common): use product-specific commit attribution

[c8dhjp4tyv-bit]

Summary

• derive git commit attribution from the compile-time FREEBUFF_MODE flag
• keep Codebuff's existing footer for standard builds
• use Freebuff branding and domain for Freebuff binaries
• add regression coverage for both product variants

Fixes #997

Validation

• Freebuff build-flag attribution smoke check: passed
• targeted common tool tests: 10 passed
• common typecheck: passed
• git diff --check: passed
• Prettier check for changed files: passed
• common full test command: 1,158 passed; 37 existing checkout/snapshot failures remain in unrelated web/agent sources and one existing Zod schema expectation
• agent-runtime typecheck: existing missing agents-graveyard/researcher/researcher imports; no errors from changed files

[codebuff-team]

Good instinct and clean fix for #997: Freebuff binaries were asking the model to sign commits as Codebuff, which is wrong for a product with its own identity. The new getGitCommitGuidePrompt(isFreebuff) function is testable and the added test file (run-terminal-command-branding.test.ts) covers both variants directly, which is exactly what this repo would want for a behavior change like this.

One thing worth cleaning up before this lands: commitProductName/commitProductDomain (lines ~136-137) duplicate the exact same ternary logic that's already inside getGitCommitGuidePrompt. Since that function takes an optional isFreebuff argument, you could just call getGitCommitGuidePrompt(isFreebuffBuild) once and derive the example string from a shared value, or export the productName/productDomain pair from the function so there's a single source of truth. Right now if someone touches the Freebuff domain/name in one place they can easily miss the other.

Also worth a comment or test noting that isFreebuffBuild is read from process.env.FREEBUFF_MODE at module load time (not truly compile-time despite the comment) — if any test or runtime code mutates that env var after this module is first imported, gitCommitGuidePrompt (the pre-computed export) won't reflect it. Not a blocker, but worth flagging since the PR description calls it a compile-time flag.

Overall this is a small, well-scoped, well-tested fix and worth porting after tightening the duplication.

[c8dhjp4tyv-bit]

Addressed both cleanup points in 1283562.

• Product name/domain now come from one getCommitAttribution() helper, used by both getGitCommitGuidePrompt() and the native tool-call example. The duplicated Freebuff/Codebuff ternaries are gone.
• Clarified the FREEBUFF_MODE lifecycle in the source comment: it is injected for Freebuff builds and read once at module initialization. The tests intentionally pass an explicit product flag, so they do not depend on mutating process.env after the module has already been imported.