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/SecureBytesTest.kt

@@ -10,16 +10,16 @@ import kotlin.test.assertTrue
 /**
  * Zeroing key material once it has been used (ios#39, Android half).
  *
- * 🔴 **The claim being tested is narrow, and the tests are shaped to keep it
+ * **The claim being tested is narrow, and the tests are shaped to keep it
  * narrow.** What this buys is that a derived key is not left sitting in the
- * heap after the one moment it was needed. It is not "the key is gone" — a
+ * heap after the one moment it was needed. It is not "the key is gone", a
  * compacting collector can have moved the array, Android has compressed swap,
  * and there is no `memset_s` on the JVM. `SecureBytes` says all of that in
  * prose; these assert only what is actually true.
  *
- * 🔴 **The most valuable test here is that the derived keys did not change.**
+ * The most valuable test here is that the derived keys did not change.
  * Wiping an intermediate one line too early derives every account secret from
- * thirty-two zero bytes — which produces a perfectly consistent, perfectly
+ * thirty-two zero bytes, which produces a perfectly consistent, perfectly
  * wrong identity, silently, on every device. That is a far worse failure than
  * the leak this feature exists to narrow, so it is checked first.
  */
@@ -31,7 +31,7 @@ class SecureBytesTest {
     // ---- The failure that would matter most -----------------------------
 
     /**
-     * 🔴 The pinned vectors already cover `authSecret` and `accountKeySeed`.
+     * The pinned vectors already cover `authSecret` and `accountKeySeed`.
      * This covers the shape wiping could break without moving a vector: that
      * the two secrets from one stretch still match the two derived separately.
      * If the wipe landed between the expansions, the second would be derived
@@ -45,7 +45,7 @@ class SecureBytesTest {
     }
 
     /**
-     * ⚠️ And neither is zeroes, which is what "derived from a wiped buffer"
+     * And neither is zeroes, which is what "derived from a wiped buffer"
      * would look like. A test that only compared the two paths would pass if
      * BOTH were wrong in the same way.
      */
@@ -104,9 +104,9 @@ class SecureBytesTest {
     }
 
     /**
-     * 🔴 **The case the `finally` exists for.** A derivation that failed
+     * The case the `finally` exists for. A derivation that failed
      * half-way is exactly where the material gets forgotten, so the wipe has to
-     * survive a throw — not sit at the end of a happy path.
+     * survive a throw, not sit at the end of a happy path.
      */
     @Test
     fun `withSecret wipes when the body throws`() {
@@ -118,9 +118,9 @@ class SecureBytesTest {
     }
 
     /**
-     * ⚠️ **The honest limit, asserted rather than left to the prose.** A copy
-     * taken before the wipe is untouched by it. This is not a bug to fix — a
-     * `ByteArray` cannot reach copies of itself — and stating it as a passing
+     * The honest limit, asserted rather than left to the prose. A copy
+     * taken before the wipe is untouched by it. This is not a bug to fix, a
+     * `ByteArray` cannot reach copies of itself, and stating it as a passing
      * test stops anybody reading `wipe` as stronger than it is.
      */
     @Test