fix: repair dead-URL redirects and add 301s for removed doc versions

[moonming]

Problem

Matomo (Apache Analytics, site 17) recorded 11,401 Page-Not-Found visits in 2026-06-14..07-11 (+485% vs the prior period). Probing every URL in the top-120 404 inventory against the live site shows 92 are still broken today, in four classes:

1. Self-inflicted: the version-less ingress-controller rules in .htaccess still redirect to 1.8.0/... — but 1.8.0 is no longer built (only the newest release is published since chore(website): clean up doc/blog workspaces + open homepage links in new tab #2066-era pruning), so our own redirects generate 404s. They even hijack /docs/ingress-controller/FAQ/ and /upgrade/, which exist again as real pages in the current IA.
2. Removed sub-project doc versions: ingress-controller 0.4.0–1.8.0, docker apisix-*/apisix-dashboard-*, apisix 2.1–2.5 — still linked from search results and external sites.
3. Bare landing directories (/docs/apisix/, /docs/apisix/plugins/, /docs/ingress-controller/, …) return 403 (no index page) while receiving real traffic.
4. Removed/renamed pages: the dashboard docs are gone from the site entirely; /docs/apisix/stand-alone; GitHub-style paths.

Fix

• Retarget the stale version-less ingress rules to their closest pages in the current IA (concepts/references → api-reference, deployments → install, tutorials → per-page or overview, upgrade → upgrade-guide); delete the FAQ hijack.
• Add version-stripping 301s for removed sub-project versions — renamed pages chain onto the retargeting rules as a second hop. The apisix project itself is excluded (3.10+ are still built; its 2.x/3.x legacy redirects are handled at the infra layer).
• Redirect dashboard docs to /docs/apisix/dashboard/, bare landing dirs to real entry pages, plus two renamed-path fixes.

Verification (local httpd, mod_alias + this exact .htaccess)

• 89 of 92 currently-broken URLs terminate at a live-200 page within ≤2 hops.
• Zero redirect loops (5-hop chase on every URL).
• /docs/ingress-controller/1.8.0/FAQ/ chains to /FAQ/, which becomes a real page once this deploys (the hijack rule is removed in the same change).
• A 38-URL control set (all current sub-project pages from the sitemap + apisix latest/versioned/next docs + hub pages) passes through with no redirect — no false positives.
• Intentionally not covered: /v2 (95 hits, ambiguous intent — no defensible target) and one single-hit CHANGELOG.md path.

Follows up on #2070 (versioned-docs canonical); together these address the two P0 technical-SEO items from the GSC/Matomo analysis.

[moonming]

Independent audit verdict: MERGE (0 HIGH). The one MEDIUM — the new strip rules funneled traffic into four pre-existing redirects whose targets (/docs/apisix/how-to-build/, /docs/apisix/architecture-design/plugin-config/) are themselves 404 — is addressed in bc20491: retargeted to building-apisix/ and terminology/plugin-config/ (en+zh, all four verified 200), bare removed ingress version dirs now chain to overview via (.*), and the misleading ordering comment is fixed. Local-httpd regression re-run after the amend: 92-URL suite terminates at live-200 in ≤2 hops, 0 loops, control set untouched.