feat(audio): add verified AAC-LC encoding and reject invalid prototype output

packages/audio/NATIVE_AAC.mdadded+41-0

Changes to packages/audio/NATIVE_AAC.md

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	1	+# Native AAC-LC encoding
	2	+
	3	+`src/encoding/native_aac.{c,h,zig}` is Home's opt-in streaming AAC-LC adapter.
	4	+It links the standalone FDK AAC library directly, without FFmpeg/Libav. The C
	5	+boundary uses the installed headers and opaque handles; no FDK layouts are
	6	+redeclared in Zig. Home's adapter is MIT; the FDK library retains its own license.
	7	+
	8	+The older `AacEncoder` and `AacFullEncoder` prototypes emitted envelope bytes or
	9	+fixed-width coefficients as if they were AAC. Their encode entry points now
	10	+return `UnsupportedLegacyEncoder`. Configuration helpers remain available;
	11	+use `audio.NativeAacEncoder` or `audio.encoding.native_aac.Encoder` for real AAC.
	12	+The old prototype's partial-allocation cleanup is also fixed.
	13	+
	14	+Compile `native_aac.c` with the system compiler, include the installed FDK header
	15	+root and link `fdk-aac`. Instantiate with an explicit sample rate, mono/stereo
	16	+channels and bitrate in bits/s. Supported rates are 8, 11.025, 12, 16, 22.05, 24,
	17	+32, 44.1 and 48kHz. Bitrate range is 16–320kb/s; unsupported combinations fail.
	18	+No resampling, HE-AAC, implicit input device access or ADTS transport is included.
	19	+
	20	+`encode` accepts 1–1024 S16LE interleaved frames and returns the number consumed
	21	+plus an optional raw access unit. Retain and feed any unconsumed input. Borrowed
	22	+packet bytes expire at the next call. Fixed input/output buffers bound memory;
	23	+there is no frame-sized growing history. Serialize calls on each encoder.
	24	+
	25	+The returned `Info` supplies the real AudioSpecificConfig, frame length and
	26	+codec delay in samples. Keep it with the stream. Drain `flush` until `null`, then
	27	+close. Encoding after drain fails. A codec failure poisons subsequent calls.
	28	+The muxer must account for codec delay and final zero padding; do not timestamp
	29	+packets from callback time or assume the codec delay is 1024/2048 samples.
	30	+
	31	+Validation uses FDK 2.0.3 at commit
	32	+`716f4394641d53f0d79c9ddac3fa93b03a49f278`. Targeted tests exercise partial PCM,
	33	+configuration bytes, delayed drain, padding coverage and state rejection on Zig
	34	+0.15.2 and Home's development toolchain. Independent camera integration decodes
	35	+with FAAD2 and checks waveforms, segment sample counts and MP4 edit timelines.
	36	+See `.github/workflows/native-aac.yml`; no hardware performance claim is made.
	37	+
	38	+```sh
	39	+zig test packages/audio/src/encoding/native_aac_test.zig \
	40	+ packages/audio/src/encoding/native_aac.c -lc -lfdk-aac
	41	+```