Remove machine-writing tells from comments and docs

Emoji markers, markdown bold inside code comments, and em-dashes are
gone from source comments, string literals, scripts, Gradle files and
the markdown docs. Counted before and after:

  emoji markers   2680 -> 1 (the emoji picker's own list, which is the feature)
  em-dashes       2490 -> 9 (table placeholders and fenced code)

Two warning glyphs in user-facing strings in ChatScreens.kt are removed
as well; the sentences say the same thing without them. Two backtick
test names carried an em-dash and now carry a comma.

Nothing else changed. 1208 tests pass, counted from the result XML.
The three obfs4 interop tests are opted out with OBFS4_INTEROP_OPTOUT=1
for this run, as their own message instructs when no bridge is set up.

CONTRIBUTING gets a four-line rule so it does not grow back.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

engine/src/test/kotlin/io/flamenet/e2e/QrCodeRenderForDecodingTest.kt

@@ -8,13 +8,13 @@ import kotlin.test.Test
 /**
  * Renders QR codes to PNG so an INDEPENDENT decoder can read them back.
  *
- * 🔴 **The only honest way to test an encoder we wrote ourselves.** A wrong QR
+ * The only honest way to test an encoder we wrote ourselves. A wrong QR
  * still looks like a QR; asserting the matrix against values this same code
  * produced proves nothing except that it is deterministic. So this writes real
  * images and `Scripts/verify-qr.swift` decodes them with CoreImage's detector,
  * which shares no line of code with `QrCode`.
  *
- * ⚠️ Not an assertion by itself — it is the fixture half. It passes as long as
+ * Not an assertion by itself, it is the fixture half. It passes as long as
  * the encoder does not throw; the verdict comes from the decoder.
  */
 class QrCodeRenderForDecodingTest {
@@ -55,7 +55,7 @@ class QrCodeRenderForDecodingTest {
             "flamenet:fnid:kx7q2m",                                     // v1
             "flamenet:fnid:" + "a".repeat(52) + "@relay1.flamenet.io",   // a real address
             "flamenet:fnid:" + "b".repeat(52) + "@" + "long".repeat(8) + ".example.com",
-            // ⚠️ Exactly full, version by version: data codewords minus the
+            // Exactly full, version by version: data codewords minus the
             // mode nibble and character count. The boundary is where an
             // off-by-one in the terminator or the padding shows up, and it is
             // the one place a wrong encoder still produces a scannable-looking
@@ -66,10 +66,10 @@ class QrCodeRenderForDecodingTest {
             "x".repeat(62),    // v4
             "x".repeat(84),    // v5
             "x".repeat(106),   // v6
-            "x".repeat(122),   // v7 — first version with a version-information block
-            "x".repeat(152),   // v8 — two block groups of different sizes
+            "x".repeat(122),   // v7, first version with a version-information block
+            "x".repeat(152),   // v8, two block groups of different sizes
             "x".repeat(180),   // v9
-            "x".repeat(213),   // v10 — the largest this encoder makes
+            "x".repeat(213),   // v10, the largest this encoder makes
         )
     }
 }