fix(lakebase): follow next_page_token when listing Postgres projects

[karen-amaya]

Summary

_lookup_via_postgres_api calls GET /api/2.0/postgres/projects once without following next_page_token. That endpoint paginates at 10 projects/page, so in workspaces with more than 10 Postgres projects, an project past page 1 is invisible to this lookup — causing the misleading error "No Lakebase Autoscaling endpoint matched... legacy Provisioned instances are not supported", even with a valid, correctly-permissioned project.

Confirmed in production (2026-09-04): the project was on page 2 of 19. Fix: loop over next_page_token until exhausted.

Linked Issue / milestone

Closes #160

Plan

N/A — single-file fix, no formal plan doc for this one.

Type of change

• feat — new feature
• fix — bug fix
• docs — documentation only
• refactor — no behaviour change
• test — tests only
• perf — perf improvement
• ci / build / chore — tooling

Author checklist

• Conventional Commit PR title (<type>(<scope>): <subject>).
• changelogs/<today>.log updated with title + context + numbered changes + files + test result.
• Tests added or modified for every behaviour change.
• uv run pytest tests/<scope>/ green locally.
• pre-commit run --all-files clean (or skipped hooks documented).
• If src/agents/** or any MLflow-traced LLM path changed:
  • SPEC.md present in .planning/<slug>/.
  • tests/eval/datasets/<agent>/dataset.jsonl has ≥20 examples (new) or ≥10 (change).
  • MLflow eval run URI in PR body below.
  • Judge score ≥ baseline + delta, or explicit waiver here.
• If src/mcp-server/** changed: uv run pytest tests/mcp/ -m mcp green.
• No gsd-* references re-introduced.

MLflow eval run

Test plan

• uv run pytest tests/ -m "not e2e and not property and not eval" --cov-fail-under=90
• Per-package coverage thresholds (scripts/check_coverage.py) green for touched packages.
• If new MCP tool: uv run pytest tests/mcp/integration/test_tool_schemas.py includes it.

Reviewer hint

See docs/PR_REVIEW_CHECKLIST.md. Numbered items map 1:1 to comments — #3: missing OntoBricksError subclass for new condition is more useful than "fix error handling".

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