fix(sweep): close small gaps and doc drift (bare event.listen, kb --version, llm UX)

[v0ropaev]

What

A cleanup cycle: every small leftover found across recent cycles, closed in one pass (12 audited findings).

Functional micro-features

• events: the bare from sqlalchemy.event import listen [as alias]; listen(...) call-form is now extracted when the import table proves the called name IS sqlalchemy.event.listen (precision-first; any other bare listen stays skipped). Closes the last call-form documented gap; events extractor_version 2 → 3; Tier-1 events oracle grows the bare registration (12 → 13 tests).
• kb --version — eager typer callback over the dynamic kb.__version__.
• PR-fetch memoization (GitHubPRProvider): one network call per PR per run; failures never stick.

CLI UX

• describe/mine: friendly "install the llm extra" message when the SDK is missing (was a raw ModuleNotFoundError); the "no LLM API key" message names the selected provider.

Regression closed

• Tier-1 API gate: two routes stacked on ONE handler sharing ONE response model (identical evidence spans) are two artifacts with distinct ids — the fastapi twin of the events/entities identity-v1 collision, flagged "fix when convenient" back when identity v2 shipped (fix(ids): fold logical_key into artifact_id (identity rule v2) #24). Proven safe, pinned by a gate.

Docs drift

README ("future" business-process extractor de-futured; events gaps; llm extra + KB_LLM_MODEL + OPENAI_BASE_URL/OpenRouter path — verified live this session; Docker EXTRAS="--extra llm" note), DESIGN events rows, CLI docstrings (mine --prs).

Checks

Suite 122 → 124 passed, 1 skipped; headline HARD gates stay fifteen; ruff + mypy --strict clean; kb --version → 0.8.0.