feat: Layer 2 device library system with TMP36 reference driver

Add embedded device library registry with full lifecycle management,
automated test integration, and pin assignment workflow.

Library system:
- Library registry embedded in binary via include_dir! (same as templates)
- library.toml metadata format: name, version, bus type, pins, provided files
- anvil add <name> extracts headers to lib/drivers/<name>/, test files to test/
- anvil remove <name> cleans up all files, config entries, and include paths
- anvil lib lists installed libraries with status
- anvil lib --available shows registry with student-friendly wiring summary
- [libraries] section in .anvil.toml tracks installed libraries and versions
- CMake auto-discovers lib/drivers/*/ for include paths at configure time

TMP36 analog temperature sensor (reference implementation):
- TempSensor abstract interface (readCelsius/readFahrenheit/readRaw)
- Tmp36Analog: real hardware impl via Hal::analogRead with configurable Vref
- Tmp36Mock: programmable values, read counting, no hardware needed
- Tmp36Sim: deterministic noise via seeded LCG for repeatable system tests
- test_tmp36.cpp: 21 Google Test cases covering mock, analog, sim, polymorphism
- TMP36 formula: voltage_mV = raw * Vref_mV / 1024, temp_C = (mV - 500) / 10

Automated test integration:
- Library test files (test_*.cpp) route to test/ during extraction
- CMakeLists.txt auto-discovers test_*.cpp via GLOB, builds each as own target
- anvil remove cleans up test files alongside driver headers
- Zero manual CMake editing: add library, run test --clean, tests appear

Pin assignment integration:
- anvil add <name> --pin A0 does extract + pin assignment in one step
- Without --pin, prints step-by-step wiring guidance with copy-paste commands
- anvil pin --audit flags installed libraries with unassigned pins
- Audit works even with zero existing pin assignments (fixed early-return bug)
- LibraryMeta helpers: wiring_summary(), pin_roles(), default_mode()
- Bus-aware guidance: analog pins, I2C bus registration, SPI with CS selection

UX improvements:
- anvil lib --available shows "Needs: 1 analog pin (e.g. A0)" not raw metadata
- anvil add prints app code example, test code example, and next step
- anvil pin --audit prints exact commands to resolve missing library pins
- anvil remove shows test file deletion in output

Files added:
- libraries/tmp36/library.toml
- libraries/tmp36/src/tmp36.h, tmp36_analog.h, tmp36_mock.h, tmp36_sim.h
- libraries/tmp36/src/test_tmp36.cpp
- src/library/mod.rs

Files modified:
- src/lib.rs, src/main.rs, src/commands/mod.rs
- src/commands/lib.rs (add/remove/list/list_available with --pin support)
- src/commands/pin.rs (audit library pin warnings, print_library_pin_warnings)
- src/project/config.rs (libraries HashMap field)
- templates/basic/test/CMakeLists.txt.tmpl (driver + test auto-discovery)

Tests: 254 total (89 unit + 165 integration)
- 12 library/mod.rs unit tests (registry, extraction, helpers)
- 2 commands/lib.rs unit tests (class name derivation)
- 30+ new integration tests covering library lifecycle, pin integration,
  audit flows, file routing, CMake discovery, config roundtrips, ASCII
  compliance, polymorphism contracts, and idempotent add/remove cycles

libraries/tmp36/library.toml

@@ -0,0 +1,15 @@
+[library]
+name = "tmp36"
+version = "0.1.0"
+description = "TMP36 analog temperature sensor"
+
+[requires]
+bus = "analog"
+pins = ["data"]
+
+[provides]
+interface = "tmp36.h"
+implementation = "tmp36_analog.h"
+mock = "tmp36_mock.h"
+simulation = "tmp36_sim.h"
+test = "test_tmp36.cpp"