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/PQVectorTest.kt

@@ -10,17 +10,17 @@ import kotlin.test.assertNotEquals
 /**
  * The hybrid handshake against the published known-answer vector.
  *
- * 🔴 **This is the only test here worth much.** Every other assertion about
+ * This is the only test here worth much. Every other assertion about
  * ML-KEM in this module compares Bouncy Castle to itself: seeds round-trip,
- * ciphertexts open, sizes are right — all true of an implementation that is
+ * ciphertexts open, sizes are right, all true of an implementation that is
  * internally consistent and agrees with nobody. The vector was generated by the
  * normative JavaScript engine and is replayed by the Swift one, so matching it
  * is the claim that actually matters: a phone can start a post-quantum session
  * with an iPhone, and neither has to take our word for it.
  *
- * The specific thing at risk is the **seed**. FIPS 203 keygen takes `d ‖ z`,
+ * The specific thing at risk is the seed. FIPS 203 keygen takes `d ‖ z`,
  * and this engine stores only those 64 bytes and re-derives everything from
- * them — so if BC ordered or expanded them differently from CryptoKit, every
+ * them, so if BC ordered or expanded them differently from CryptoKit, every
  * cross-platform session would fail at the first message with nothing pointing
  * at the cause. The vector settles it byte for byte.
  */
@@ -31,8 +31,8 @@ class PQVectorTest {
         // does it: this module lives both as a subtree of the app repo and as a
         // repo of its own beside the engine.
         //
-        // ⚠️ Fails rather than skips when nothing is found. A conformance test
-        // that quietly stops conforming is worth less than no test at all —
+        // Fails rather than skips when nothing is found. A conformance test
+        // that quietly stops conforming is worth less than no test at all,
         // the file listing still says the handshake is checked.
         val candidates = listOfNotNull(
             System.getenv("FLAMENET_PQ_VECTORS"),
@@ -49,7 +49,7 @@ class PQVectorTest {
     private fun hex(bytes: ByteArray) = bytes.joinToString("") { "%02x".format(it) }
 
     /**
-     * 🔴 **The cross-implementation check.** The vector publishes a seed and
+     * The cross-implementation check. The vector publishes a seed and
      * the public key the normative engine derived from it; deriving a different
      * one here is the failure that would make every Android↔iPhone post-quantum
      * session fail on the first message, and nowhere near this code.
@@ -75,7 +75,7 @@ class PQVectorTest {
      * Everything is exercised at once and that is the point: the four
      * agreements, their order, the KEM secret going last, the v2 info string,
      * and the associated data. A vector that only checked the KEM would pass
-     * while the concatenation order was wrong — and the two engines would still
+     * while the concatenation order was wrong, and the two engines would still
      * never talk.
      */
     @Test
@@ -111,7 +111,7 @@ class PQVectorTest {
     }
 
     /**
-     * 🔴 **A downgrade must not produce a key the other side accepts.** v1's
+     * A downgrade must not produce a key the other side accepts. v1's
      * `DH1‖DH2‖DH3‖DH4` and v2's `DH1‖DH2‖DH3‖SS` are both 128 bytes, so
      * without the info string changing with the version they are
      * indistinguishable KDF inputs (§12.5). Asserted against the published
@@ -135,7 +135,7 @@ class PQVectorTest {
     }
 
     /**
-     * ⚠️ The associated data binds the ciphertext, so a relay that swapped one
+     * The associated data binds the ciphertext, so a relay that swapped one
      * cannot leave the session looking untouched. ML-KEM's implicit rejection
      * means decapsulation itself will not complain.
      */