docs: add CONTRIBUTING.md + partner-submission PR template

[RJK134]

Summary

Establishes a public acceptance bar for the three categories of contribution this repo gets:

1. Fixes — bug fixes, typos, doc tweaks (no preamble needed)
2. New content — new skills, commands, agents
3. Partner submissions — third-party MCP connectors and partner-built plugins

The first two are already broadly understood. The third has been the source of a queue of ~20 open PRs with no documented bar, no consistent triage, and no clear signal to submitters about what gets accepted vs declined.

What this PR adds

• CONTRIBUTING.md — full guide, including:
  • Workflow for each category (paths, sync commands, version-bump behavior)
  • 8-row acceptance criteria table for partner submissions (live endpoint, no bundled creds, license-compatible, scoped to FSI verticals, etc.)
  • Explicit "we don't accept" list (aspirational integrations, retail-only tooling, etc.)
  • Review process and timing expectations
• .github/PULL_REQUEST_TEMPLATE/partner-submission.md — partner submitters opt in via ?template=partner-submission.md on the new-PR URL. Walks the criteria as checkboxes.
• README.md — Contributing section now points at CONTRIBUTING.md for the full guide.

Triage recommendations for the existing partner-PR queue

This PR doesn't close any partner PRs — those decisions need maintainer judgment. But for reference, here's a recommended call for each based on the new criteria (column meanings: ✅ accept after review, 🟡 needs discussion, ❌ close with reason, 🔁 needs rebase onto post-#81 layout).

MCP connectors (small surface, low-risk)

PR	Vendor	Recommendation	Notes
#187	Box	✅	Broad doc-store fit; minimal surface (.mcp.json + README)
#180	Quartr	✅	Strong fit for equity-research; already wires into earnings-reviewer
#181	Longbridge	🟡	Brokerage data; legitimate but niche — confirm vendor scope is FSI
#156	TensorFeed	🟡	Free public-domain data; thin signal on production usage — verify per criteria 1

Partner-built plugins (full plugin, higher bar)

PR	Vendor	Recommendation	Notes
#186	FundOS / VantedgeAI	🟡	Fund-ops for emerging VC/credit; valid scope; verify partner-agreement signatory status
#183	Valuein	🟡	SEC EDGAR + smart-money; overlaps Daloopa — confirm distinct value
#172 + #107	Phronesis	🟡	Submitted in two PRs (skills, MCP) — ask submitter to consolidate
#198	certnode-provenance	🟡	Compliance/provenance layer; useful but unclear if it's a fit for marketplace or better as standalone
#159 / #143	KAELUM	❌	"Commerce currency" — not an FSI workflow product per criteria; duplicate submissions of same vendor
#38	Chinese stock market analysis tool	❌	Retail-targeted; non-English plugin without i18n strategy
#49	URai	❌	Explicitly retail-investor focused — see "we don't accept"

Pre-#81 layout (need rebase before re-review)

These submissions have legitimate content but were authored before the agent-plugins/vertical-plugins restructure. They place files at top-level (e.g. partner-built/ not plugins/partner-built/).

PR	What it adds	Recommendation
#72	Synechron credit memo plugin	🔁 Worth asking author to rebase — credit memos are a real gap
#71	FinBrain alt-data plugin	🔁 Ask to rebase; evaluate per criteria after
#31	sspdf PDF generation	🔁 Ask to rebase; useful infra
#17	private-credit plugin	🔁 Significant content; ask to rebase. Aligns with credit/lending gap noted in plan Phase 8
#8	venture-capital plugin	🔁 Ask to rebase; aligns with VC gap
#33	Equity-research company-research agent	🔁 Significant content; ask to rebase. Overlaps existing market-researcher; review for distinct value

Verification

• python3 scripts/check.py clean (OK — 80 file(s) checked, 0 issues.)
• No new manifest entries; pure docs PR
• Pre-commit hook ran with no plugin version-bumps (no .claude-plugin/plugin.json touched)

Test plan

• On merge: link CONTRIBUTING.md from the marketplace listing or organization-level contributor guide
• Maintainer reviews the triage table above and processes the queue in batches

🤖 Generated with Claude Code