stp: vendor-style per-port config + status (path cost, p2p, designated info)

Bring the Spanning Tree page in line with a typical managed switch's
per-port panel. Configuration gains the full-range path cost (raw
0..200000000, 0 = auto, replacing the old 1000x-scaled byte), a
point-to-point admin control (auto/on/off), and the priority is now a
0..240 step-16 dropdown. A new status table shows, per port, the Port
State, Role, Designated Bridge / Port ID / Cost (learned from received
BPDUs, kept per port and aged via the BPDU age), Operational Edge and
Operational Point-to-Point.

The designated fields fall back to presenting this switch as the
segment's designated bridge when no fresh BPDU has been heard (so a
quiet port shows our own bridge-id, as the vendor UIs do). /stp.json
carries the packed hex fields plus our own MAC for that fallback.

Space: reclaim BANK2 for the above by moving rtl837x_pins to HOME and
compacting leds_dump into a register-address table (~800B); bandwidth
returns to BANK1. No BANK3 - hardware-verified that PSBANK > 2 crashes
this SoC at boot (a bricked unit and an SPI-programmer recovery earlier
today); a warning to that effect is now in rtl837x_lldp.c.

Hardware-verified: cost 200000000 and p2p off round-trip through the CLI
and JSON, the status table populates correctly with STP enabled (all
ports Forwarding/Designated, oper-edge and oper-p2p True), LACP 3f/3f
and the LAN unaffected.

(cherry picked from commit 2ec62072f061dc9e78bc821ba1c297cb6819e206)

html/config.js

@@ -27,10 +27,11 @@ const conf_cmds = [
   /^stp\s+version\s+(rstp|stp)$/,
   /^stp\s+port\s+\d{1,2}\s+(on|off)$/,
   /^stp\s+port\s+\d{1,2}\s+edge\s+(on|off|auto)$/,
-  /^stp\s+port\s+\d{1,2}\s+cost\s+\d{1,3}$/,
+  /^stp\s+port\s+\d{1,2}\s+cost\s+\d{1,9}$/,
   /^stp\s+port\s+\d{1,2}\s+prio\s+\d{1,3}$/,
   /^stp\s+port\s+\d{1,2}\s+guard\s+(none|bpdu|root)$/,
   /^stp\s+port\s+\d{1,2}\s+filter\s+(on|off)$/,
+  /^stp\s+port\s+\d{1,2}\s+p2p\s+(auto|on|off)$/,
   /^igmp\s+(on|off)$/,
   /^mtu\s+\d{1,2}\s+\d+$/,
   /^bw\s+(in|out)\s+\d{1,2}\s+\S+$/,
@@ -55,7 +56,7 @@ const conf_overwrite = [
   /^laghash\b/,
   /^isolate\s+\d{1,2}\b/,
   /^stp\s+(prio|hello|maxage|fwd|txhold|version|failsafe)\b/,
-  /^stp\s+port\s+\d{1,2}\s+(edge|cost|prio|guard|filter)\b/,
+  /^stp\s+port\s+\d{1,2}\s+(edge|cost|prio|guard|filter|p2p)\b/,
   /^igmp\b/,
   /^mtu\s+\d{1,2}\b/,
   /^bw\s+(in|out)\s+\d{1,2}\b/,