feat(subagent): show agent emoji header before output

[birdmanmandbir]

Summary

• Add emoji field to AgentFrontmatter in internal/sync/frontmatter.go so canonical subagent .md files can declare an emoji
• Before streaming output, ttal subagent run <name> prints \n<emoji> <name>\n to stderr as a visual header
• ttal explore prints 🔭 explore [--project/--repo/--url/--web <target>] header before each run
• Added printAgentHeader helper to cmd/subagent.go shared by both commands
• Added emojis to all 8 canonical subagent templates in templates/docs/agents/

Subagent	Emoji
plan-reviewer	📋
pr-code-reviewer	🔍
pr-code-simplifier	✨
pr-comment-analyzer	💬
pr-principles-reviewer	📐
pr-silent-failure-hunter	🕵️
pr-test-analyzer	🧪
pr-type-design-analyzer	🏗️

Test plan

• make ci passes (fmt, vet, lint, test, build)
• ttal subagent run pr-code-reviewer "..." shows 🔍 pr-code-reviewer header before output
• ttal explore "..." --project ttal-cli shows 🔭 explore --project ttal-cli header
• ttal sync deploys updated subagent files with emoji in frontmatter

[birdmanmandbir]

PR Review: feat(subagent): show agent emoji header before output

Reviewed by: pr-code-reviewer, pr-principles-reviewer, pr-silent-failure-hunter

Critical Issues

None

Important Issues

None

Observations

• Output to stderr — printAgentHeader correctly writes to os.Stderr, keeping stdout clean for pipe-friendly usage. ✓
• Placement timing — header is printed after config/limits resolution but before provider build, so provider errors won't produce a spurious header. ✓
• Empty emoji guard — printAgentHeader handles empty emoji gracefully (falls back to name-only). ✓
• Consistent coverage — all five explore variants (--project, --repo, --url, --web, general) correctly wired with 🔭 emoji and descriptive labels. ✓
• exploreOpts label fallback — the if label == "" guard in runExploreAgent is defensive and correct, even though all current callers supply non-empty labels. ✓
• Non-breaking field addition — Emoji string on AgentFrontmatter deserializes to "" for agents without the field, handled gracefully downstream. ✓
• Agent template emojis — all 8 agent files received semantically appropriate emojis.

VERDICT: LGTM