fix: harden intraday evidence provenance

[KCNyu]

What changed

• normalize the intraday insights sidecar before dashboard publication, retaining only model-owned narrative and stamping a harness-owned UTC generated_at
• keep missing or malformed sidecars warn-only so deterministic report delivery continues
• extend the shared numeric provenance advisory to %, pp, x/×, and σ, with unit-specific context matching
• update the shared skill and canonical cron payload so the model is no longer instructed to author infrastructure time
• repair the numeric contract tests' stale import path so both real postflight integrations execute instead of skipping

Evidence

• replaying trajectory 993d3509-08fb-43be-834a-91f13087f5b7 now produces exactly one advisory: 2.3x; all context-backed percentage and pp claims pass
• the +8h model timestamp is overwritten with UTC before publish_data_plane() runs
• malformed sidecar JSON still delivers the report and records insights_sidecar=false

Verification

• pytest -q tests/test_numeric_claims.py tests/test_intraday_prose_assembly.py tests/test_sync_cron_payloads.py tests/test_cron_contracts.py — 73 passed
• mutation checks: replacing unit-specific matching with the flat number set fails the 2.3x regression; trusting the model timestamp fails the future-time regression
• required remote checks must pass before merge

Closes #482
Closes #483