Use merged Markdown fix and simplify CDN verification

[tiye]

Changes

• Use exact merged Markdown fix 1256d550445bf69573bc9e53bbccbea1ddcb0530 (Align Markdown 0.4.47 with strict Calcit 0.27 and COS gates Respo/respo-markdown.calcit#61), not an invented published release. Calcit/procs remain latest stable 0.27.0.
• Delete standalone CDN build verification; COS action v1.1.1 built-in public verification remains the only upload checker.
• Remove repeated migration/type/dynamic/deprecation diagnostics; keep strict entry/public contracts, original quality baseline and existing business tests.
• Existing menu business test now renders each original history instead of only selecting the first, including the previously failing Vue internals inline-code messages. No new test file or paid TTS request.
• Development jointly watches Calcit/Vite with initial compile; builds compile once. Isolate frontend previews by PR/run/attempt.
• No snapshot, data, speech adapter, worker implementation or quality baseline changes. Preserve original production prefix, upload policy, fonts, storage keys and server sync paths.

Verification

• Current head 3cbbf68: official Linux CI https://github.com/b-conf/hestory/actions/runs/36860732058 succeeded.
• Caps/toolchain, immutable install, canonical guards, strict init/reload, 50/50 public definitions and original quality baseline passed. Caps accurately warns that Markdown is an immutable commit without SemVer release metadata.
• Actual codegen/Vite and all 10 existing business tests passed, including each historical message rendering and speech/worker fixture behavior.
• COS v1.1.1 internally verified HTML 623, CSS 532, JS 1166263 and emitted transcode worker 862 bytes at b-conf/hestory/pr/28/36860732058/1/.
• Server deployment skipped on this PR. No production deployment, browser speech or paid service verification claimed.