Redesign phase C: claim flow, limited manage page, device protocol

The frame-claiming pipeline, end to end. Firmware: every request now
carries ?id=<12-hex STA MAC> via build_url (mirrored in build_ota_url),
and the captive portal's success page became a redirect that hands the
user's browser to <server>/claim?device_id=... after ~7s -- enough time
for the phone to drop the provisioning AP while the device reboots.
The server pushes a per-frame device token through /frame/config during
a one-time handshake; the firmware persists it to NVS (a dedicated
single-key write that deliberately doesn't reset the connected-once
flag or WiFi cache) and prefers it over the provisioned shared token
from the next request on. Config response buffer grows 256->512. Both
board variants compile clean; new firmware also works against an old
server (which ignores ?id=) and old firmware against this server (the
phase A legacy mapping), so either deploy order survives.

Server: /claim lands the captive-portal redirect -- claim-gated signup
(a valid unclaimed/unregistered device id IS the enrollment invitation),
pending claims for the user-beats-the-frame race (auto-attached at
self-registration, 24h expiry), and a waiting page that refreshes until
the frame checks in. Unclaimed/unconfigured frames get a rendered
instruction placeholder with a QR from /frame/image (200, never an
error loop) -- new qrcode dep, placeholder shares the exact
quantize/pack path photos use.

The on-frame manage QR now resolves to a limited no-login page: scans
of / carrying device credentials (new ?id&token or the legacy shared
token) 303 to /m/<manage_token>, which allows exactly view queue,
show-next, advance, back, and scoped thumbnails -- no settings, no
removal, no other frames. Full control means logging in.

One real protocol hole found by simulating full wake cycles: after
self-registration the device could never authenticate again (the wake
cycle fetches the image BEFORE /frame/config delivers its token).
require_device now treats the id itself as the credential until the
first authenticated request flips device_token_ack -- the same trust
level as open registration, closing permanently once the handshake
completes.

firmware/main/wifi_provisioning.h

@@ -11,13 +11,37 @@
 #define FRAME_CFG_TOKEN_MAX_LEN 64
 #define FRAME_AP_PASSWORD_LEN 10
 
+#define FRAME_DEVICE_ID_LEN 12 /* 6-byte STA MAC as lowercase hex */
+
 typedef struct {
     char sta_ssid[FRAME_CFG_SSID_MAX_LEN + 1];
     char sta_password[FRAME_CFG_PASSWORD_MAX_LEN + 1];
     char toolsserver[FRAME_CFG_SERVER_MAX_LEN + 1];
-    char access_token[FRAME_CFG_TOKEN_MAX_LEN + 1]; /* optional; matches the server's MANAGEMENT_TOKEN */
+    char access_token[FRAME_CFG_TOKEN_MAX_LEN + 1]; /* optional; legacy shared MANAGEMENT_TOKEN */
+    /* Per-frame token issued by the server via GET /frame/config after
+     * this device first introduces itself by id -- preferred over
+     * access_token once present (see frame_client.c's build_url). Not
+     * set at the captive portal; empty until the server pushes one. */
+    char device_token[FRAME_CFG_TOKEN_MAX_LEN + 1];
 } frame_config_t;
 
+/**
+ * This device's stable identity as reported to the server (?id= on every
+ * request): the full 6-byte STA MAC as 12 lowercase hex chars. Derived
+ * from the same MAC the provisioning AP SSID suffix comes from; never
+ * stored. out must hold at least FRAME_DEVICE_ID_LEN + 1 bytes.
+ */
+void frame_device_id_get(char *out, size_t out_size);
+
+/**
+ * Persists (only) the server-issued per-frame device token -- called
+ * from the wake cycle when GET /frame/config delivers one. Deliberately
+ * touches nothing else: unlike frame_config_save() it must not reset
+ * the connected-once flag or invalidate the WiFi fast-connect cache,
+ * since nothing about the network changed.
+ */
+void frame_config_set_device_token(const char *token);
+
 /**
  * Loads the saved home-network config from NVS.
  * Returns ESP_ERR_NVS_NOT_FOUND if the device has never been provisioned.