fix(pg): auto-migrate schema on pg serve startup

[tlmaloney]

Summary

• Run EnsureSchema before CheckSchemaCompat in pg serve so missing tables (e.g. tool_result_events after upgrading from 0.16.x to 0.17.0) are created automatically
• Read-only PG roles gracefully fall through to the existing compat check error
• Add TestEnsureSchemaMigratesLegacySchema integration test that simulates a legacy schema upgrade

Closes #251

Test plan

• make test passes
• make test-postgres passes (exercises TestEnsureSchemaMigratesLegacySchema)
• Manual: upgrade from 0.16.x schema, verify pg serve starts without manual SQL

🤖 Generated with Claude Code

[roborev-ci]

roborev: Combined Review (2709de4)

Verdict: One medium-severity startup reliability issue should be addressed before merge.

Medium

• cmd/agentsview/pg.go:243: Unexpected EnsureSchema failures are currently downgraded to a warning and startup continues into CheckSchemaCompat. If migration fails after partial DDL, or on schema objects that CheckSchemaCompat does not verify, pg serve can start against a partially migrated schema and fail later in less obvious ways.
  • Suggested fix: Abort startup on any non-read-only EnsureSchema error, and keep warning-only handling limited to the explicitly accepted read-only case.

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Synthesized from 3 reviews (agents: codex, gemini | types: default, security)

[roborev-ci]

roborev: Combined Review (93381ce)

Verdict: No medium-or-higher issues found; the change looks good to merge.

All reviewed agents agreed the diff is clean. The update to run a best-effort schema migration before compatibility checks, with read-only fallback behavior and added legacy-schema test coverage, did not surface any Medium, High, or Critical findings.

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Synthesized from 3 reviews (agents: codex, gemini | types: default, security)