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/basic-toml/tests/invalid/datetime-malformed-no-leads.toml

@@ -0,0 +1 @@
+no-leads = 1987-7-05T17:45:00Z

vendor/basic-toml/tests/invalid/datetime-malformed-no-secs.toml

@@ -0,0 +1 @@
+no-secs = 1987-07-05T17:45Z

vendor/basic-toml/tests/invalid/datetime-malformed-no-t.toml

@@ -0,0 +1 @@
+no-t = 1987-07-0517:45:00Z

vendor/basic-toml/tests/invalid/datetime-malformed-with-milli.toml

@@ -0,0 +1 @@
+with-milli = 1987-07-5T17:45:00.12Z

vendor/basic-toml/tests/invalid/duplicate-key-table.toml

@@ -0,0 +1,5 @@
+[fruit]
+type = "apple"
+
+[fruit.type]
+apple = "yes"

vendor/basic-toml/tests/invalid/duplicate-keys.toml

@@ -0,0 +1,2 @@
+dupe = false
+dupe = true

vendor/basic-toml/tests/invalid/duplicate-table.toml

@@ -0,0 +1,8 @@
+[dependencies.openssl-sys]
+version = "0.5.2"
+
+[dependencies]
+libc = "0.1"
+
+[dependencies]
+bitflags = "0.1.1"

vendor/basic-toml/tests/invalid/duplicate-tables.toml

@@ -0,0 +1,2 @@
+[a]
+[a]

vendor/basic-toml/tests/invalid/empty-implicit-table.toml

@@ -0,0 +1 @@
+[naughty..naughty]

vendor/basic-toml/tests/invalid/empty-table.toml

@@ -0,0 +1 @@
+[]

vendor/basic-toml/tests/invalid/float-no-leading-zero.toml

@@ -0,0 +1,2 @@
+answer = .12345
+neganswer = -.12345

vendor/basic-toml/tests/invalid/float-no-suffix.toml

@@ -0,0 +1 @@
+a = 1.2f

vendor/basic-toml/tests/invalid/float-no-trailing-digits.toml

@@ -0,0 +1,2 @@
+answer = 1.
+neganswer = -1.

vendor/basic-toml/tests/invalid/key-after-array.toml

@@ -0,0 +1 @@
+[[agencies]] owner = "S Cjelli"

vendor/basic-toml/tests/invalid/key-after-table.toml

@@ -0,0 +1 @@
+[history] guard = "sleeping"

vendor/basic-toml/tests/invalid/key-empty.toml

@@ -0,0 +1 @@
+ = 1

vendor/basic-toml/tests/invalid/key-hash.toml

@@ -0,0 +1 @@
+a# = 1

vendor/basic-toml/tests/invalid/key-newline.toml

@@ -0,0 +1,2 @@
+a
+= 1

vendor/basic-toml/tests/invalid/key-open-bracket.toml

@@ -0,0 +1 @@
+[abc = 1

vendor/basic-toml/tests/invalid/key-single-open-bracket.toml

@@ -0,0 +1 @@
+[

vendor/basic-toml/tests/invalid/key-space.toml

@@ -0,0 +1 @@
+a b = 1

vendor/basic-toml/tests/invalid/key-start-bracket.toml

@@ -0,0 +1,3 @@
+[a]
+[xyz = 5
+[b]

vendor/basic-toml/tests/invalid/key-two-equals.toml

@@ -0,0 +1 @@
+key= = 1

vendor/basic-toml/tests/invalid/string-bad-byte-escape.toml

@@ -0,0 +1 @@
+naughty = "\xAg"

vendor/basic-toml/tests/invalid/string-bad-escape.toml

@@ -0,0 +1 @@
+invalid-escape = "This string has a bad \a escape character."

vendor/basic-toml/tests/invalid/string-bad-line-ending-escape.toml

@@ -0,0 +1,3 @@
+invalid-escape = """\
+    This string has a non whitespace-character after the line ending escape. \  a
+"""

vendor/basic-toml/tests/invalid/string-byte-escapes.toml

@@ -0,0 +1 @@
+answer = "\x33"

vendor/basic-toml/tests/invalid/string-no-close.toml

@@ -0,0 +1 @@
+no-ending-quote = "One time, at band camp

vendor/basic-toml/tests/invalid/table-array-implicit.toml

@@ -0,0 +1,14 @@
+# This test is a bit tricky. It should fail because the first use of
+# `[[albums.songs]]` without first declaring `albums` implies that `albums`
+# must be a table. The alternative would be quite weird. Namely, it wouldn't
+# comply with the TOML spec: "Each double-bracketed sub-table will belong to 
+# the most *recently* defined table element *above* it."
+#
+# This is in contrast to the *valid* test, table-array-implicit where
+# `[[albums.songs]]` works by itself, so long as `[[albums]]` isn't declared
+# later. (Although, `[albums]` could be.)
+[[albums.songs]]
+name = "Glory Days"
+
+[[albums]]
+name = "Born in the USA"

vendor/basic-toml/tests/invalid/table-array-malformed-bracket.toml

@@ -0,0 +1,2 @@
+[[albums]
+name = "Born to Run"

vendor/basic-toml/tests/invalid/table-array-malformed-empty.toml

@@ -0,0 +1,2 @@
+[[]]
+name = "Born to Run"

vendor/basic-toml/tests/invalid/table-empty.toml

@@ -0,0 +1 @@
+[]

vendor/basic-toml/tests/invalid/table-nested-brackets-close.toml

@@ -0,0 +1,2 @@
+[a]b]
+zyx = 42

vendor/basic-toml/tests/invalid/table-nested-brackets-open.toml

@@ -0,0 +1,2 @@
+[a[b]
+zyx = 42

vendor/basic-toml/tests/invalid/table-whitespace.toml

@@ -0,0 +1 @@
+[invalid key]

vendor/basic-toml/tests/invalid/table-with-pound.toml

@@ -0,0 +1,2 @@
+[key#group]
+answer = 42

vendor/basic-toml/tests/invalid/text-after-array-entries.toml

@@ -0,0 +1,4 @@
+array = [
+  "Is there life after an array separator?", No
+  "Entry"
+]

vendor/basic-toml/tests/invalid/text-after-integer.toml

@@ -0,0 +1 @@
+answer = 42 the ultimate answer?

vendor/basic-toml/tests/invalid/text-after-string.toml

@@ -0,0 +1 @@
+string = "Is there life after strings?" No.

vendor/basic-toml/tests/invalid/text-after-table.toml

@@ -0,0 +1 @@
+[error] this shouldn't be here

vendor/basic-toml/tests/invalid/text-before-array-separator.toml

@@ -0,0 +1,4 @@
+array = [
+  "Is there life before an array separator?" No,
+  "Entry"
+]

vendor/basic-toml/tests/invalid/text-in-array.toml

@@ -0,0 +1,5 @@
+array = [
+  "Entry 1",
+  I don't belong,
+  "Entry 2",
+]