chore(release): 0.3.0

[caohy1988]

Release PR for 0.3.0.

What this PR does

• Bumps `pyproject.toml` version from `0.2.3` to `0.3.0`.
• Renames the existing `## [Unreleased]` section to `## [0.3.0] - 2026-05-15` in `CHANGELOG.md`.
• Adds a Release highlights summary at the top of the 0.3.0 section so readers can see the three major workstreams at a glance.
• Re-opens an empty `## [Unreleased]` section above 0.3.0 for post-release work.

No code changes. All entries in the 0.3.0 block were already merged on `main` between #122 (the 0.2.3 cut) and #160 (the Migration V5 final).

Why 0.3.0 (minor bump) and not 0.2.4

The Unreleased block has 24 top-level `Added` entries spanning three full feature workstreams:

1. Compiled structured extractors — Phase C (#75) — deterministic source generation, JSON-to-plan parsing, LLM-driven plan resolution, retry orchestrator, runtime fallback wiring, runtime extractor-registry adapter, orchestrator call-site swap, compile-and-measure utility, revalidation harness, BigQuery-table bundle mirror, new `bqaa-revalidate-extractors` CLI with `--events-bq-query-file`, and the operational rollout guide.
2. Ontology runtime reader (#58) — new `ontology_runtime` module: `OntologyRuntime`, `EntityResolver` Protocol with `ExactEntityResolver` / `LabelSynonymResolver`, `ConceptIndexLookup` with fingerprint-strict verification and stable failure codes.
3. Binding + extraction validation toolkit (#76, #105) — new `validate_extracted_graph` / `validate_binding_against_bigquery` Python APIs, `bq-agent-sdk binding-validate` CLI, `ontology-build --validate-binding` / `--location` flags.

That's substantial new feature surface, all additive, no breaking changes. SemVer minor bump is the correct call.

What's NOT in the 0.3.0 changelog block

By design — these are example/demo additions, not SDK API changes:

• A2A Joint Lineage demo and its evolution (PRs #132, #133, #135, #141, #145, #147, #149)
• Migration V5 / MAKO four-guarantee notebook (PRs #155, #157, #160)

The Release-highlights summary mentions both demos as examples shipped alongside the release, with cross-references to the tracking issues (#107, #129). If reviewers want explicit per-PR entries for the demos, easy to add — let me know.

Verification

• `pyproject.toml` parses cleanly: `python3 -c "import tomllib; print(tomllib.loads(open('pyproject.toml').read())['project']['version'])"` → `0.3.0`.
• `CHANGELOG.md` structure validated: top-level headers are `[Unreleased]` → `[0.3.0] - 2026-05-15` → `[0.2.3] - 2026-04-27` → `[0.2.2]` → `[0.2.1]` (chronological + monotonic).
• Diff is exactly two files (+45 / -1 lines), no other modifications.

Post-merge

Once this lands on main, the next step is the actual release: tag `v0.3.0` on the merge commit and trigger the PyPI publish flow (whichever release pipeline the repo uses — confirm with a maintainer before tagging).

Test plan

• `pyproject.toml` parses; version is `0.3.0`.
• `CHANGELOG.md` headers are well-formed, monotonic, and dated.
• Empty `[Unreleased]` placeholder is re-opened above 0.3.0 for post-release work.
• No code changes — only `pyproject.toml` and `CHANGELOG.md` touched.
• CI green on this PR.

[caohy1988]

Release-note completeness fix — pushed in `bbe88fb`

Per the release-note review, four user-visible public-API additions that landed in the 0.3.0 window weren't explicitly release-noted in the initial bump. Added them as four bullets at the top of `### Added` in the 0.3.0 section:

Entry	Source	PR
`A2A_INTERACTION` typed view (`adk_a2a_interactions`) — surfaces caller-side A2A delegation rows with JSON-extracted lineage columns and the `receiver_session_id_from_response` COALESCE	`src/bigquery_agent_analytics/views.py:215`	#136
`CodeEvaluator.context_cache_hit_rate(...)` + CLI — Gemini context-cache prefix-hit rate evaluator with cold-start/warm thresholds and `fail_on_missing_telemetry` switch, wired through `bqaa evaluate --evaluator context_cache_hit_rate`	`src/bigquery_agent_analytics/evaluators.py:522`, `src/bigquery_agent_analytics/cli.py:343`	#114
`gm compile --emit-concept-index` / `--concept-index-table` — fingerprint-stamped concept-index emission (the writer surface the ontology runtime reader verifies against)	`src/bigquery_ontology/cli.py:354`	#92
`ontology-build --skip-property-graph` — materialize node and edge tables without issuing the `CREATE OR REPLACE PROPERTY GRAPH` statement, for users who own their property-graph DDL	`src/bigquery_agent_analytics/cli.py:1332`	#108

Took your "four bullets under `### Added`" option rather than introducing a fifth subsection. Each bullet cites the source file path + line range and the originating PR so reviewers can verify.

Verification:

• `uv build` (or `python -m build`) still produces `bigquery_agent_analytics-0.3.0` sdist/wheel artifacts.
• `pyproject.toml` parse-check still clean: version `0.3.0`.
• `CHANGELOG.md` headers still monotonic: `[Unreleased]` → `[0.3.0] - 2026-05-15` → `[0.2.3] - 2026-04-27`.
• Diff is exactly one file (+39 lines), no other changes.

PR is now at:

• Head: `bbe88fb`
• Diff vs main: 2 files, +84/-1
• CHANGELOG completeness: all user-visible public-API additions since 0.2.3 now explicitly release-noted.

Holding for CI as you suggested.