Intraday message feed can duplicate items and lacks after-hours labels

[simplerjiang]

• Source: .automation/sprint.md V048-DEBT-11 and .automation/buglist.md runtime data watch #44.
• Impact: Users can see repeated or time-context-ambiguous intraday messages.
• Repro:
  1. Open stock intraday message feed.
  2. Inspect repeated titles/timestamps and early-morning records.
• Expected: Deduplicated feed with clear session/after-hours labeling.
• Actual: Backlog records duplicate and label issues.
• Claim: Assign stocks/news owner.
• Repair: Strengthen dedup key and session label logic.
• Verification: Parser/unit tests plus browser feed check.