chore: run hotspots delta check in pre-commit hook

[stephenc222]

Summary

• Adds a hotspots analyze . --mode delta --policy --format text step to .githooks/pre-commit, alongside the existing cargo fmt/clippy/test steps — dogfoods the tool on its own repo at commit time.
• Uses the exact invocation hotspots init --hooks already recommends (its own official hook template), just wired into the existing local pre-commit hook instead of a separate pre-push/.pre-commit-config.yaml setup, matching this repo's existing hook mechanism (.githooks/, activated via make install-hooks).
• No baseline snapshot exists for commit history by default, so on a machine without one yet, policy evaluation is silently skipped (tool's own documented behavior) rather than failing the commit — verified locally.

Test plan

• Ran the updated hook directly: fmt, clippy, 549 unit tests, and the new hotspots analyze step all pass
• Committed through the real hook (not bypassed) to confirm it doesn't block a normal commit

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