chore: remove legacy quant-scholar artifacts and .gitai; rename logo

[keli-wen]

Summary

Remove pre-pivot quant-scholar machinery and other stale artifacts, and rename the active logo asset to drop editing-process cruft from its filename. This is repository housekeeping with no Python or public-behavior changes.

Deleted:

• wiki/ (index.md ~1.5MB, embedding.md) — quant-scholar auto-generated arxiv-list output.
• docs/papers.md, docs/quant-scholar.json — the quant-scholar paper list and its backing data.
• .github/workflows/quant_scholar.yml, .github/workflows/update_paper_links.yml — the daily/weekly crons that regenerate the files above. They also invoke a quant_scholar.py that is not tracked in this repository, so they cannot succeed here anyway.
• docs/EMBEDDINGS.md — documents the removed pre-pivot EmbeddingBlock runtime.
• docs/ENVIRONMENT_SETUP.md — orphan with no inbound references; environment setup is already covered by README.md and CONTRIBUTING.md.
• .gitai/ — an external AI commit/PR message generator. It produced the non-English commit subject dcf724b. Commit conventions belong in the quantmind-dev skill and, going forward, in an enforced commit-msg hook.

Renamed:

• assets/quantmind-new-orange-shaved.png -> assets/quantmind-wordmark.png, with the README.md reference updated.

docs/README.md and docs/library.md are intentionally kept: they are the user-facing component catalog and library guide, referenced by AGENTS.md, CLAUDE.md, the quantmind-dev skill, and CONTRIBUTING.md.

Related Issue

Part of the cleanup that motivated issue #134 (agent-facing context map + convention-enforcing git hooks); the removed .gitai tool is the direct cause of the non-English commit that the commit-msg hook will prevent going forward. This PR is cleanup only and does not complete that issue, which stays open.

Verification

• bash scripts/verify.sh passes (ruff format + ruff check + basedpyright + lint-imports + pytest --cov; 405 passed, 85.66% coverage).
• No live-network smoke test applies: this PR removes documentation, workflows, and tooling config and renames an asset; it changes no public operation or source.
• Confirmed no remaining references to the deleted paths or the old asset name via repository grep.

Checklist

• The title uses English Conventional Commit format: type(scope): summary.
• The related issue or design discussion is linked when applicable.
• bash scripts/verify.sh passes.
• Every applicable live-network component smoke test passes, or this PR states why none applies.
• Public behavior has focused tests, an example, and documentation where applicable.
• The PR is complete, small, and contains no unrelated changes.