Fix Codex goal continuation transcript handling

[tpn]

Fixes #868.

Classifies Codex goal-continuation wrapper messages as internal/system content during parsing so they no longer persist as ordinary user turns or inflate user-message counts.

Adds read-path fallbacks for legacy stored rows by recognizing both current <codex_internal_context source="goal"> and older <goal_context> wrappers in backend/frontend system-message checks. HTML export now applies the same filtering and keeps focused transcript selection from being affected by legacy goal-context rows.

This bumps the parser data version to 55. Multi-host PostgreSQL deployments should upgrade pg serve and all pushers together, because older agentsview binaries reject PG rows written by a newer parser data version.

[roborev-ci]

roborev: Combined Review (69c4679)

HTML export has one medium-severity visibility regression; security review found no issues.

Medium

• Location: internal/server/export.go:678
  Problem: The new HTML export filter drops every db.IsSystemPrefixed user message, which also removes promoted Claude boundary rows such as continuations, interruptions, task notifications, and stop-hook feedback that the SPA intentionally keeps visible via source_subtype.
  Fix: Restrict the export filter to the Codex goal-context prefixes, or mirror the frontend visibility rules by preserving visible system subtypes before applying prefix fallback.

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Panel: ci_default_security | Synthesis: codex, 6s | Members: codex_default (codex/default, done, 3m55s), codex_security (codex/security, done, 58s) | Total: 4m59s