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>

obfs4/build.gradle.kts

@@ -6,23 +6,23 @@ plugins {
 repositories { mavenCentral() }
 
 dependencies {
-    // 🔴 **The whole reason this port is small.** The Swift implementation had
+    // The whole reason this port is small. The Swift implementation had
     // to hand-write SipHash-2-4, XSalsa20 and Poly1305 because CryptoKit
     // exposes none of them, and its own field arithmetic because Apple gives
     // nothing below X25519. BouncyCastle has all four, vetted and
     // constant-time where it matters: `X25519Field` (including `sqrtRatioVar`,
     // exactly the primitive Elligator2 needs), `XSalsa20Engine`, `Poly1305`.
     //
-    // ⚠️ That means the two clients do NOT share an implementation. They share
+    // That means the two clients do NOT share an implementation. They share
     // the vectors and the live interop harness, which is what actually keeps
-    // them honest — see `Obfs4VectorTest`.
+    // them honest, see `Obfs4VectorTest`.
     //
     // Already a dependency of `:engine`, for the same class of reason: taking a
     // vetted constant-time implementation over hand-rolling arithmetic on a
     // secret scalar.
     implementation("org.bouncycastle:bcprov-jdk18on:1.79")
 
-    // ⚠️ compileOnly: the transport must not drag OkHttp into anything that
+    // compileOnly: the transport must not drag OkHttp into anything that
     // does not already have it. `:client` supplies the real one.
     compileOnly("com.squareup.okhttp3:okhttp:4.12.0")
     testImplementation("com.squareup.okhttp3:okhttp:4.12.0")