[AZ-626] Decompose complete: 47 tasks + docs + module layout

Greenfield Steps 1-6 baseline for the autopilot rewrite from legacy
Qt/C++ to a Rust workspace.

- Remove legacy Qt/C++ tree (ai_controller, drone_controller,
  misc/camera, python_scaffold, root Dockerfile, autopilot.pro,
  legacy main.py / requirements.txt).
- Add _docs/00_problem (problem, restrictions, acceptance criteria,
  security approach, input data + fixtures).
- Add _docs/01_solution/solution_draft01.
- Add _docs/02_document (architecture, system-flows, data_model,
  glossary, decision-rationale, deployment, 13 component descriptions,
  tests/ specs, FINAL_report, module-layout).
- Add _docs/02_tasks/todo with 47 task specs (AZ-640..AZ-686, one
  bootstrap + 46 component tasks) and _dependencies_table.md.
- Add .cursor/rules/artifact-srp.mdc (single-responsibility rule for
  canonical _docs artifacts).
- Track autodev state in _docs/_autodev_state.md (Step 6 completed,
  ready for Step 7 Implement).

Jira: bootstrap AZ-626; component epics AZ-627..AZ-639; tasks
AZ-640..AZ-686. Total complexity 173 points across 12 epics.

Co-authored-by: Cursor <cursoragent@cursor.com>

_docs/02_tasks/todo/AZ-658_frame_ingest_decoder.md

@@ -0,0 +1,72 @@
+# Frame Decoder (NVDEC + Software Fallback)
+
+**Task**: AZ-658_frame_ingest_decoder
+**Name**: H.264/265 decoder (NVDEC primary, software fallback) + monotonic timestamps
+**Description**: Decode H.264/265 to raw frames using NVDEC on Jetson Orin Nano, with software fallback. Stamp each frame with a monotonic capture timestamp + sequence number at the earliest practical point in the pipeline.
+**Complexity**: 5 points
+**Dependencies**: AZ-640_initial_structure, AZ-657_frame_ingest_rtsp_session
+**Component**: frame_ingest
+**Tracker**: AZ-658
+**Epic**: AZ-627
+
+## Problem
+
+Every frame downstream needs a monotonic capture timestamp so `movement_detector` can detect telemetry skew. Decoding must use the hardware decoder (NVDEC on Jetson) where present and fall back to software otherwise, without changing the emitted `Frame` shape. Decode errors on a single frame must be dropped (counted), not abort the stream — cold-start latency is observable once but not an alert by itself.
+
+## Outcome
+
+- `FrameDecoder::decode(packet) -> Result<Frame, DecodeError>` emits a `Frame { seq, capture_ts_monotonic, decode_ts_monotonic, pixels: Arc<Bytes>, width, height, pix_fmt, ai_locked }`.
+- NVDEC code path is used when available; software fallback otherwise (selection is automatic and observable in health).
+- Single-frame errors are dropped and counted as `decode_errors_total`; the stream is never aborted on a single frame.
+- Cold-start latency (first-frame decode time) is surfaced as `decode_ms_first_frame` once per session open.
+- Health surface: `decode_ms_p50`, `decode_ms_p99`, `decoder_backend ∈ {NVDEC, Software}`, `decode_errors_total`.
+
+## Scope
+
+### Included
+- NVDEC binding (via Jetson Multimedia API or GStreamer `nvv4l2decoder`).
+- Software decoder fallback (FFmpeg `libavcodec`).
+- Monotonic timestamping at the earliest point in the decode pipeline.
+- Sequence-number generation (monotonic u64 per session).
+- Single-frame error handling.
+
+### Excluded
+- RTSP session lifecycle (task 18).
+- Multi-consumer publisher (task 20).
+
+## Acceptance Criteria
+
+**AC-1: Software-path decode of a sample stream**
+Given a sample H.264 RTSP stream at 1080p / 30 fps and a host without NVDEC
+When the decoder runs for 10 s
+Then ≥285 frames are emitted; `decoder_backend = "Software"`; sequence numbers are strictly monotonic.
+
+**AC-2: NVDEC-path selection on Jetson**
+Given the host has NVDEC available
+When the decoder is initialized
+Then `decoder_backend = "NVDEC"`; functional correctness is identical to software path.
+
+**AC-3: Single-frame decode error does not abort the stream**
+Given the input contains one corrupted frame
+When the decoder runs
+Then that single frame is dropped, `decode_errors_total` increments by 1, and subsequent frames continue to be emitted.
+
+**AC-4: Monotonic timestamps**
+Given a sequence of decoded frames
+When their `capture_ts_monotonic` is read
+Then values are strictly monotonically increasing.
+
+## Non-Functional Requirements
+
+**Performance**
+- End-to-end RTSP-rx → publish ≤30 ms p99 on Jetson Orin Nano (per `description.md §8`); decoder portion of that budget ≤20 ms p99.
+
+**Reliability**
+- Single-frame errors do not abort the stream.
+- Cold-start latency surfaced once; not an alert.
+
+## Runtime Completeness
+
+- **Named capability**: H.264/265 decode (NVDEC primary, software fallback) — production decode path required.
+- **Production code that must exist**: real NVDEC binding; real software fallback; real monotonic timestamping.
+- **Unacceptable substitutes**: software-only decode on Jetson is acceptable as fallback but the NVDEC code path MUST exist (otherwise the latency target cannot be met).