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/StorySetTest.kt

@@ -35,7 +35,7 @@ class StorySetTest {
     }
 
     /**
-     * 🔴 One envelope per item. An array of attachments would fail the
+     * One envelope per item. An array of attachments would fail the
      * single-`att` guard on any build predating §6.23 and render the whole set
      * as a message in the conversation.
      */
@@ -62,7 +62,7 @@ class StorySetTest {
         assertEquals(listOf("s1", "s2", "s3"), groups[0].map { it.id })
     }
 
-    /** ⚠️ `n` says three; two came. Render what arrived. */
+    /** `n` says three; two came. Render what arrived. */
     @Test
     fun `a partly arrived set is still rendered`() {
         val groups = Vault.groupedStories(listOf(
@@ -71,7 +71,7 @@ class StorySetTest {
         assertEquals(2, groups[0].size)
     }
 
-    /** ⚠️ Two singles must not collide just because neither has a set id. */
+    /** Two singles must not collide just because neither has a set id. */
     @Test
     fun `two sets and a single stay apart`() {
         val groups = Vault.groupedStories(listOf(
@@ -82,7 +82,7 @@ class StorySetTest {
 
     // -- Expiry ---------------------------------------------------------------
 
-    /** 🔴 The earliest wins, so a sender cannot outlive part of its own set. */
+    /** The earliest wins, so a sender cannot outlive part of its own set. */
     @Test
     fun `a set expires at its earliest stamp`() {
         assertEquals(100.0, Vault.setExpiry(listOf(
@@ -91,7 +91,7 @@ class StorySetTest {
             item(3, "a", expires = 200.0))))
     }
 
-    /** ⚠️ A zero means "never" and must not be read as "expires at the epoch". */
+    /** A zero means "never" and must not be read as "expires at the epoch". */
     @Test
     fun `a zero stamp does not expire the whole set`() {
         assertEquals(500.0, Vault.setExpiry(listOf(
@@ -114,7 +114,7 @@ class StorySetTest {
         override fun names() = records.keys.toList()
     }
 
-    /** ⚠️ The set survives a reload, or a relaunch scatters every sequence. */
+    /** The set survives a reload, or a relaunch scatters every sequence. */
     @Test
     fun `the set survives the vault round trip`() {
         val vault = Vault(MapStorage(),