refactor(campaign): finish Proposer migration — uniform optimize-a-surface DX

[drewstone]

What

Finishes the Proposer migration so the optimize-a-surface DX is uniform: every optimizer is a factory xProposer(opts): SurfaceProposer exported from /campaign, drivable by selfImprove({ proposer }).

The two flagship proposers already conform on main (shipped in 83505fb):

• skillOptProposer(opts): SurfaceProposer — factory at src/campaign/proposers/skill-opt.ts, wraps applySkillPatch / runSkillOpt internals behind the contract (also exposes the patch-native proposePatches used by the runSkillOpt preset). Exported from /campaign.
• gepaProposer — at src/campaign/proposers/gepa.ts, exported from /campaign AND re-exported from /contract.

This PR closes the last gap — the Proposer name collision: the behavior-fuzzing Proposer<S> (src/fuzz/types.ts) is a different concept from the optimization SurfaceProposer. Renamed it to MutationProposer<S> (matches its sole value, mutationProposer) so SurfaceProposer is unambiguously THE optimization proposer. A @deprecated Proposer<S> alias keeps the public ./fuzz export back-compatible.

Verified

• pnpm run typecheck clean, pnpm run build clean, pnpm run lint 0 errors.
• pnpm test: 247 files, 2533 passed, 2 skipped.
• Runtime probe against built dist/campaign: import { gepaProposer, skillOptProposer } from "@tangle-network/agent-eval/campaign" resolves to real functions; both produce objects satisfying SurfaceProposer (.kind gepa/skill-opt, .propose); skillOptProposer exposes proposePatches.
• ./fuzz .d.ts still exports both MutationProposer and the deprecated Proposer alias.

Version

Additive exports + alias-only on the public surface → minor bump 0.96.5 → 0.97.0 (package.json + clients/python/pyproject.toml + __init__.py together).

[tangletools]

✅ Auto-approved PR — 6e508ab1

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_{tangletools · auto-approval · reason: blanket_auto_approve · 2026-06-22T22:31:39Z}