chore(release): 0.4.0 — retail-returns, ADK 2.0 event types, expanded quality report

[caohy1988]

Release bigquery-agent-analytics 0.4.0

Bumps pyproject.toml 0.3.4 → 0.4.0 and rolls the unreleased changes since v0.3.4 into a dated [0.4.0] CHANGELOG section. Minor bump — every change is a backward-compatible addition.

Included since v0.3.4

• retail-returns seed-events scenario (feat(seed_events): add retail-returns multi-agent scenario with token/latency telemetry (#313) #314) — multi-agent refund/exchange trace with LLM_REQUEST/LLM_RESPONSE token-usage and latency telemetry; lights up v_llm_response (usage_*_tokens / total_ms / ttft_ms) on seed. Deterministic; decision/decision-realistic unchanged and byte-identical.
• ADK 2.0 event types across the SDK type surfaces (feat(views): register ADK 2.0 event types across SDK type surfaces (#211) #311) — typed views for the adk-2.0 producer: minimum plan to unblock mid-June customer cutover #293 event types + header-only workflow-boundary types; TOOL_COMPLETED extended with long-running pair keys.
• SystemEvaluator (Refactor: Rename CodeEvaluator to SystemEvaluator #121) — preferred name for deterministic/code metrics; CodeEvaluator retained as a backward-compatible alias.
• Expanded quality report (Quality report: dimensions, correction analysis, execution traces, golden-Q&A grounding, and version filtering #174) — dimensions, correction analysis, execution traces, golden-Q&A grounding, version filtering.

Verification

• pyproject.toml version == 0.4.0; CHANGELOG [Unreleased] emptied, new [0.4.0] - 2026-06-18 section added. No other files pin the old version.
• Diff is release-only: CHANGELOG.md + pyproject.toml.

After merge, tag v0.4.0 on main per the usual release flow.

[caohy1988]

Release Review

Findings: none.

Scope check: clean. The diff is release-only: pyproject.toml and CHANGELOG.md.

I re-checked the release mechanics and content:

• pyproject.toml bumps the root package from 0.3.4 to 0.4.0.
• The release workflow verifies the published release tag by comparing vX.Y.Z to project.version, so v0.4.0 will match this PR.
• src/bigquery_agent_analytics/__init__.py has no separate version constant to update.
• Referenced feature PRs are merged into main: #314, #311, #121, and #174.
• The remaining 0.3.4 mentions in docs/examples are minimum-version guidance for features introduced in 0.3.4, not stale package pins.
• CHANGELOG.md moves the previously-unreleased entries into [0.4.0] - 2026-06-18 and leaves [Unreleased] empty for the next cycle.
• Current PR checks are green across build, format, scan, and the Python test matrix.

Approved. This is ready to merge, then tag v0.4.0 from main.