feat(entrypoints): framework-aware detection for Python, Rust, Solidity

Stage 2 of entrypoint detection. Covers the highest-value syntactic
markers across three languages:

Python:
  - Flask/FastAPI/aiohttp HTTP decorators (@app.route, @router.get, etc.)
  - Click/Typer CLI commands (@click.command, @app.command on Typer)
  - Celery task handlers (@app.task, @shared_task)

Rust:
  - actix-web/rocket HTTP attributes (#[get("/")], #[post("/")], etc.)
  - FFI exports (#[no_mangle] and pub extern "C")
  - Async main entrypoints (#[tokio::main], #[actix_web::main])

Solidity:
  - External/public function visibility
  - fallback()/receive() signatures (detector ready; parser doesn't emit
    these nodes yet — test documents the deferred parser gap)

Detection runs automatically between the main() heuristic and
pyproject-script passes in QueryEngine.from_directory. A shared
_SourceCache avoids re-reading files for each node.

Adds docs/entrypoint-patterns.md — a reference document covering all
17 supported languages with detection signals, trust/asset defaults,
grep-ready patterns, and gotchas. Serves as the spec for the remaining
detectors (JS/TS/Go/Java/PHP/Ruby/C#/C/C++/Haskell/Erlang/Cairo/Circom/
Miden) which are planned as follow-ups.

13 new tests covering every framework detector plus a regression guard
for the Solidity parser gap.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: tob-scott-a