Add reconciler and ingest modules with CLI driver

reconciler: generic resource state machine — BFS pathfinding from current
to wanted state, dependency constraints, event/periodic tick model.
reconciler_cli exercises it with simulated device/transport/stream resources.

ingest: V4L2 capture module — open device, negotiate MJPEG format, MMAP
buffer pool, capture thread with on_frame callback. start/stop lifecycle
designed for reconciler management. Transport-agnostic: caller wires
on_frame to proto_write_video_frame.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

include/ingest.h

@@ -0,0 +1,66 @@
+#pragma once
+
+#include <stdint.h>
+#include "error.h"
+
+typedef struct Ingest_Handle Ingest_Handle;
+
+/*
+ * Called from the capture thread for each dequeued frame.
+ * data points into the mmap'd buffer — valid only for the duration of the call.
+ * Do not free data; copy if you need to retain it beyond the callback.
+ */
+typedef void (*Ingest_Frame_Fn)(
+	const uint8_t *data, uint32_t len,
+	int width, int height, uint32_t pixfmt,
+	void *userdata);
+
+/*
+ * Called from the capture thread when a fatal error terminates the capture loop.
+ * After this callback returns, the thread exits and the handle is in a stopped
+ * state (equivalent to after ingest_stop).  msg is a static string.
+ */
+typedef void (*Ingest_Error_Fn)(const char *msg, void *userdata);
+
+struct Ingest_Config {
+	const char      *device;   /* e.g. "/dev/video0" */
+	uint32_t         pixfmt;   /* V4L2_PIX_FMT_MJPEG etc.; 0 = auto (best MJPEG) */
+	int              width;    /* 0 = auto */
+	int              height;   /* 0 = auto */
+	Ingest_Frame_Fn  on_frame;
+	Ingest_Error_Fn  on_error; /* may be NULL */
+	void            *userdata;
+};
+
+/*
+ * Open the V4L2 device, negotiate format, allocate MMAP buffers.
+ * Does NOT start streaming.  on_frame must not be NULL.
+ */
+struct App_Error ingest_open(const struct Ingest_Config *cfg, Ingest_Handle **out);
+
+/*
+ * Enable streaming and start the capture thread.
+ * Must be called on a handle in the OPEN (not streaming) state.
+ */
+struct App_Error ingest_start(Ingest_Handle *h);
+
+/*
+ * Signal the capture thread to stop and block until it exits.
+ * Disables streaming.  The handle returns to the OPEN state and can be
+ * restarted with ingest_start or released with ingest_close.
+ */
+struct App_Error ingest_stop(Ingest_Handle *h);
+
+/*
+ * Release MMAP buffers and close the device fd.
+ * Must be called only when the handle is not streaming (before ingest_start
+ * or after ingest_stop).
+ */
+void ingest_close(Ingest_Handle *h);
+
+/* Query the negotiated format — valid after a successful ingest_open. */
+int      ingest_width(const Ingest_Handle *h);
+int      ingest_height(const Ingest_Handle *h);
+uint32_t ingest_pixfmt(const Ingest_Handle *h);
+int      ingest_fps_n(const Ingest_Handle *h);
+int      ingest_fps_d(const Ingest_Handle *h);