fix(feed): suppress committed semantic web search

[Juliusolsson05]

Summary

• suppress finalized live web-search semantic blocks once their committed rollout tool row owns the same response item id
• stop empty finalized reasoning/thinking blocks from counting as renderable semantic units
• update render diagnostics to show itemId-based committed ownership for provider-native activity blocks
• add a regression fixture based on the 2026-05-17 web-search bundle

Closes #191.

Verification

• npm run test:feed-render-model
• npm run test:semantic-committed-text
• npm run test:codex-optimistic-submit
• npm run test:ghost-fallback
• npm run test:semantic-fold-codex-replace
• npm run test:codex-semantic-channel
• npm run build

Notes

The separate Codex resume transcript failure from bundle 2026-05-17T12-04-00-107-b6c85d86 is tracked as #193. That likely needs a codex-headless resume-lineage fix and is intentionally not mixed into this renderer PR.