Clean up for public release: docs, zero warnings, no hardcoded paths

Documentation:
- docs/aacs.md — AACS encryption (1.0 + 2.0), key resolution, decrypt
- docs/udf.md — UDF 2.50 filesystem with metadata partitions
- docs/mpls.md — MPLS playlist format, STN stream table
- docs/clpi.md — CLPI clip info, EP map, sector extents
- docs/architecture.md — library module map, design principles
- docs/drive-access.md — drive sessions, SCSI transport, unlock

Code cleanup:
- Zero compiler warnings
- Removed all debug eprintln from library code
- No hardcoded private paths — KEYDB tests use KEYDB_PATH env var
- KEYDB search locations as named constants
- drive.rs: extracted create_platform(), deduplicated open methods
- lib.rs: updated doc examples to show Disc::scan() API
- Fixed UDF file reads (partition_start, not metadata_start)
- Exported KeySource from disc module

src/speed.rs

@@ -65,9 +65,7 @@ impl DriveSpeed {
             22_001..=31_000   => DriveSpeed::BD6x,
             31_001..=40_000   => DriveSpeed::BD8x,
             40_001..=49_000   => DriveSpeed::BD10x,
-            49_001..=0xFFFE   => DriveSpeed::BD12x,
-            0xFFFF            => DriveSpeed::Max,
-            _                 => DriveSpeed::Max,
+            49_001..=u16::MAX => DriveSpeed::BD12x,
         }
     }