Restyle bug-fixer agent to match PR #17053 agent conventions

[Copilot]

The bug-fixer agent (PR #17047) uses a different structure and style than the agent set in PR #17053. This aligns the bug-fixer with the established conventions so it can be merged into the same PR coherently.

No code was committed — the rewritten agent was printed in-chat as requested. Key style changes:

• Frontmatter: Removed boilerplate comments, added tools: list matching other agents
• Filename: BUG-FIXER.agent.md → bug-fixer-agent.md
• Structure: Added # Bug Fixer H1, --- separators, standalone ## Commit section at end — consistent with changelog-agent.md, validator-agent.md, etc.
• Skills reference: Switched from verbose markdown links to brief → arrow format used by feature-implementer-agent
• Tables: Converted test commands and edge-case escalation from bullet lists to tables (matches validator-agent and feature-orchestrator-agent)
• Workflow: Consolidated 9 steps + 4 appendix sections into 7 focused steps with inline cross-references — no content lost, just tighter
• Tone: Shifted from explanatory paragraphs to direct imperative style matching the other agents

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