feat: update sync workflow for per-skill release tags

[Rodriguespn]

Summary

• Updates sync-agent-skills.yml input description to reflect the new per-skill tag format (e.g. skills/supabase-v0.1.3)
• Fixes branch name in create-pull-request step — previously included the release tag verbatim, which would produce an invalid branch name once tags contain /; now uses a fixed name feat/sync-agent-skills

Related

supabase/agent-skills#97 — implements per-skill releases and triggers this sync workflow with the new tag format

🤖 Generated with Claude Code

[Rodriguespn]

Closing — the sync workflow no longer needs updating. With the new release model, the tag passed to this workflow is the root release tag (e.g. v0.1.6), same format as before. The / branch name issue that motivated this PR no longer exists.