Route support to Discussions and remove PR screenshots

[Kevinjohn]

Part of #1406 (T1). Merge predecessor: none.

• SUPPORT.md routes setup and usage questions to the Discussions Q&A category (Discussions are now on).
• The issue chooser links to Discussions instead of offering a support-question form.
• Removes .github/screenshots/. Pull requests that embedded these images use commit-pinned URLs, which keep resolving; the two that pointed at main (Center allocation popovers over visible bars #1110, Fix release E2E mismatches for segmented controls and clipped popovers #1145) were re-pinned first.

Already applied on GitHub: repository description and topics, Discussions enabled, five unused polish labels deleted, #748 closed.

Validation: integrated with the other Batch 1 branches on b04a75f5 (merge of origin/main da72918): pnpm run format:check, pnpm run docs:build (no drift) and pnpm run gate:server pass on Node 24.16.0. Independently reviewed before opening.

Merge order

1. Route support to Discussions and remove PR screenshots #1411, Add project status, comparison, testing and philosophy pages #1412, Archive changelog sections before 0.41.0-alpha.3 #1414 (independent)
2. Add a first-change path for contributors #1413 (after Archive changelog sections before 0.41.0-alpha.3 #1414), Restate the comment standard as numbered voice rules #1415, Reduce configuration and hide password MFA #1416
3. Rename SMALLSASS_ACCOUNT_ settings to CAPACITYLENS_ #1417 → Add an init command that writes the environment file #1418
4. Retire unused settings and derive engagement grouping #1419 → Move diagnostics to an Owner and Admin page #1420 → Reshape the documentation into four role guides #1421 → Use @/ for app imports that leave their folder #1422 → Consolidate server test scaffolding #1423 → Normalise server route handlers and reply messages #1424 → Apply the comment-voice rules and check them in the gate #1425 (Apply the comment-voice rules and check them in the gate #1425 also after Restate the comment standard as numbered voice rules #1415) → Name the tenant boundary account in code #1426

Merge predecessor for this PR: none.

[Kevinjohn]

Polish review: no P1/P2 findings.

• Verified the Q&A Discussions category exists (q-a), so the new SUPPORT.md and issue-chooser links resolve.
• No file in the tree still references .github/screenshots/ or support.yml.
• Prettier passes on the changed files.

Merge order for this batch: #1411, #1412, #1414 → #1413, #1415, #1416 → #1417 → #1418, #1419 → #1420 → #1421 → #1422 → #1423 → #1424 → #1425 → #1426. This PR has no predecessor.