bench: add scale benchmark suite (94 tests)

Benchmark mempalace at configurable scale (1K–100K drawers) to find
real-world performance limits. Tests cover MCP tool OOM thresholds,
ChromaDB query degradation, search recall@k, mining throughput,
knowledge graph concurrency, memory leak detection, palace boost
quantification, and Layer1 unbounded fetch behavior.

- tests/benchmarks/ with 8 test modules + data generator + report system
- Deterministic data factory with planted needles for recall measurement
- JSON report output with regression detection (--bench-report flag)
- CI benchmark job on PRs at small scale
- psutil added as dev dependency for RSS tracking

pyproject.toml

@@ -38,11 +38,11 @@ Repository = "https://github.com/milla-jovovich/mempalace"
 mempalace = "mempalace:main"
 
 [project.optional-dependencies]
-dev = ["pytest>=7.0", "ruff>=0.4.0"]
+dev = ["pytest>=7.0", "ruff>=0.4.0", "psutil>=5.9"]
 spellcheck = ["autocorrect>=2.0"]
 
 [dependency-groups]
-dev = ["pytest>=7.0", "ruff>=0.4.0"]
+dev = ["pytest>=7.0", "ruff>=0.4.0", "psutil>=5.9"]
 
 [build-system]
 requires = ["hatchling"]
@@ -64,3 +64,9 @@ quote-style = "double"
 
 [tool.pytest.ini_options]
 testpaths = ["tests"]
+pythonpath = ["."]
+markers = [
+    "benchmark: scale/performance benchmark tests",
+    "slow: tests that take more than 30 seconds",
+    "stress: destructive scale tests (100K+ drawers)",
+]