fix(seo): trailing-slash redirect variants for bare docs paths

[Mlaz-code]

Summary

• Adds trailing-slash source variants for all exact-match Vercel redirects (e.g., /quickstart/ → /en/quickstart/)
• Adds trailing-slash variants for section index paths (e.g., /en/api-reference/ → /en/api-reference/overview/)
• Adds redirects for /me and /value-bets which GSC reported as 404s
• Root cause: Vercel trailingSlash: true rewrites /foo → /foo/ before evaluating redirects, so bare-path rules never fired — the trailing-slash version 404d instead of redirecting to /en/...

Impact

• Fixes 5 GSC "Redirect error" pages
• Fixes ~5 of the 19 GSC "Not found (404)" pages
• Fixes 31 "Page with redirect" pages (redirect chains now resolve cleanly)

Test plan

• curl -sIL https://docs.sharpapi.io/concepts/arbitrage → should 301 to /en/concepts/arbitrage/ (was 308 → 404)
• curl -sIL https://docs.sharpapi.io/quickstart → should 301 to /en/quickstart/ (was 308 → 404)
• curl -sIL https://docs.sharpapi.io/en/api-reference/ → should 301 to /en/api-reference/overview/ (was 404)
• curl -sIL https://docs.sharpapi.io/me → should 301 to /en/ (was 308 → 404)

🤖 Generated with Claude Code

[Mlaz-code]

Merge gate (auto-classified): gate=smoke-passed — auto-classified by the gate-log enforcer (12min after merge, no Merge gate: audit comment found). Reviewer agent: please correct if wrong by replying with Merge gate: gate=<correct-word> — <evidence>. The audit log keys on the first such token; your correction overrides this auto-classified guess.

Posted by scripts/gate-log-enforcer.py because instruction-level rules about the gate= template aren't binding (0/N adoption); structural enforcement fills the log either way.