feat(manifestos): forge-loop manifesto suggest --from-pr feedback-loop CLI

[hadamrd]

Parent

Part of #130.

What

forge-loop manifesto suggest --from-pr <N> — the feedback-loop CLI. Reads a recently-merged fix PR (or a closed bug), analyzes the failure shape, proposes manifesto deltas as a patch.

Acceptance

• New CLI subcommand manifesto suggest.
• Reads the bug PR (via GhClient), its diff, its linked issue body, and the test files added.
• Runs a focused SDK session with the manifestos + the bug context. Output: a structured ManifestoSuggestion with proposed adds/edits + rationale citing the bug.
• Dry-run by default — prints the suggestion. --apply opens a PR against .forge/*-manifesto.md with the delta.
• Tests: against a fixture bug PR diff, assert suggestion structure + rationale references the bug.

File pointers

• src/forge_loop/manifesto_suggest.py (new)
• src/forge_loop/cli.py — subcommand
• tests/test_manifesto_suggest.py (new)