feat: add display UI with splash screen, dashboard, and RSSI sparkline

Implement full SSD1306 OLED display support:
- Splash screen on boot (1.5s) with project name, version, board
- Dashboard showing radio state, config, counters, RSSI/SNR
- RSSI history sparkline (64-sample ring buffer, 2px-wide bars)
- DisplayOn/DisplayOff host commands routed via dedicated channel
- Pure render functions against generic DrawTarget (no hardware coupling)
- Display on/off control bypasses radio task entirely

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

vendor/zerocopy/benches/split_at_dynamic_padding.x86-64.mca

@@ -0,0 +1,59 @@
+Iterations:        100
+Instructions:      1000
+Total Cycles:      404
+Total uOps:        1000
+
+Dispatch Width:    4
+uOps Per Cycle:    2.48
+IPC:               2.48
+Block RThroughput: 4.0
+
+
+Instruction Info:
+[1]: #uOps
+[2]: Latency
+[3]: RThroughput
+[4]: MayLoad
+[5]: MayStore
+[6]: HasSideEffects (U)
+
+[1]    [2]    [3]    [4]    [5]    [6]    Instructions:
+ 1      1     0.33                        mov	rax, rdi
+ 1      1     0.33                        cmp	rcx, rdx
+ 1      1     1.00                        jbe	.LBB5_2
+ 1      0     0.25                        xor	esi, esi
+ 1      1     1.00           *            mov	qword ptr [rax], rsi
+ 1      1     1.00                  U     ret
+ 1      1     1.00           *            mov	qword ptr [rax + 8], rdx
+ 1      1     1.00           *            mov	qword ptr [rax + 16], rcx
+ 1      1     1.00           *            mov	qword ptr [rax], rsi
+ 1      1     1.00                  U     ret
+
+
+Resources:
+[0]   - SBDivider
+[1]   - SBFPDivider
+[2]   - SBPort0
+[3]   - SBPort1
+[4]   - SBPort4
+[5]   - SBPort5
+[6.0] - SBPort23
+[6.1] - SBPort23
+
+
+Resource pressure per iteration:
+[0]    [1]    [2]    [3]    [4]    [5]    [6.0]  [6.1]  
+ -      -     0.99   1.00   4.00   3.01   2.00   2.00   
+
+Resource pressure by instruction:
+[0]    [1]    [2]    [3]    [4]    [5]    [6.0]  [6.1]  Instructions:
+ -      -     0.99    -      -     0.01    -      -     mov	rax, rdi
+ -      -      -     1.00    -      -      -      -     cmp	rcx, rdx
+ -      -      -      -      -     1.00    -      -     jbe	.LBB5_2
+ -      -      -      -      -      -      -      -     xor	esi, esi
+ -      -      -      -     1.00    -      -     1.00   mov	qword ptr [rax], rsi
+ -      -      -      -      -     1.00    -      -     ret
+ -      -      -      -     1.00    -     1.00    -     mov	qword ptr [rax + 8], rdx
+ -      -      -      -     1.00    -      -     1.00   mov	qword ptr [rax + 16], rcx
+ -      -      -      -     1.00    -     1.00    -     mov	qword ptr [rax], rsi
+ -      -      -      -      -     1.00    -      -     ret