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

src/main.rs

@@ -120,6 +120,41 @@ enum Commands {
         dir: Option<String>,
     },
 
+    /// Add a device library to the project
+    Add {
+        /// Library name (e.g. tmp36)
+        name: String,
+
+        /// Assign a pin during add (e.g. --pin A0)
+        #[arg(long, value_name = "PIN")]
+        pin: Option<String>,
+
+        /// Path to project directory (defaults to current directory)
+        #[arg(long, short = 'd', value_name = "DIR")]
+        dir: Option<String>,
+    },
+
+    /// Remove a device library from the project
+    Remove {
+        /// Library name (e.g. tmp36)
+        name: String,
+
+        /// Path to project directory (defaults to current directory)
+        #[arg(long, short = 'd', value_name = "DIR")]
+        dir: Option<String>,
+    },
+
+    /// List installed or available device libraries
+    Lib {
+        /// Show all available libraries (not just installed)
+        #[arg(long)]
+        available: bool,
+
+        /// Path to project directory (defaults to current directory)
+        #[arg(long, short = 'd', value_name = "DIR")]
+        dir: Option<String>,
+    },
+
     /// View pin maps, assign pins, and audit wiring
     Pin {
         /// Capability filter (pwm, analog, spi, i2c, uart, interrupt)
@@ -279,6 +314,19 @@ fn main() -> Result<()> {
                 commands::board::list_boards(dir.as_deref())
             }
         }
+        Commands::Add { name, pin, dir } => {
+            commands::lib::add_library(&name, pin.as_deref(), dir.as_deref())
+        }
+        Commands::Remove { name, dir } => {
+            commands::lib::remove_library(&name, dir.as_deref())
+        }
+        Commands::Lib { available, dir } => {
+            if available {
+                commands::lib::list_available()
+            } else {
+                commands::lib::list_libraries(dir.as_deref())
+            }
+        }
         Commands::Pin {
             name, pin, assign, remove, audit, brief,
             generate, capabilities, init_from, mode, cs, board, dir,