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>

scripts/obfs4-interop.sh

@@ -1,17 +1,17 @@
 #!/usr/bin/env bash
 # Run the Kotlin obfs4 port against real lyrebird, in both directions.
 #
-# 🔴 The only check that proves interoperability. Everything else in `:obfs4`
+# The only check that proves interoperability. Everything else in `:obfs4`
 # compares against recorded vectors or against itself, and two identically-wrong
 # ends agree perfectly.
 #
-# ⚠️ A wire-format bug shows up as SILENCE, not an error: obfs4 bridges do not
+# A wire-format bug shows up as SILENCE, not an error: obfs4 bridges do not
 # answer handshakes they cannot verify. The Kotlin side uses read timeouts and
 # reports them as "the bridge refused to answer".
 #
-# ⚠️ The Go counterparty lives in the flamenet-elligator2 checkout, which also
+# The Go counterparty lives in the flamenet-elligator2 checkout, which also
 # holds the Swift port. Both clients are pinned to the SAME reference rather
-# than to each other — two independent implementations agreeing with lyrebird is
+# than to each other, two independent implementations agreeing with lyrebird is
 # a real statement; agreeing with each other is not.
 set -euo pipefail
 cd "$(dirname "$0")/.."
@@ -46,7 +46,7 @@ echo "building the lyrebird bridge and client..."
 "$WORK/interopserver" -params "$PARAMS" -addr 127.0.0.1:0 >/dev/null 2>"$SERVER_LOG" &
 SERVER_PID=$!
 
-# ⚠️ Poll for the params file rather than sleeping. A fixed sleep is either
+# Poll for the params file rather than sleeping. A fixed sleep is either
 # flaky or slow, and on a loaded machine it is both.
 for _ in $(seq 1 100); do
     [[ -f "$PARAMS" ]] && break
@@ -55,28 +55,28 @@ for _ in $(seq 1 100); do
 done
 [[ -f "$PARAMS" ]] || { echo "the bridge never published its parameters"; exit 1; }
 
-# ⚠️ sed, not python3 or jq: the CI images for this repo cannot be assumed to
+# sed, not python3 or jq: the CI images for this repo cannot be assumed to
 # have either, and that assumption has cost red pipelines before.
 ADDRESS="$(sed -n 's/.*"address"[[:space:]]*:[[:space:]]*"\([^"]*\)".*/\1/p' "$PARAMS")"
 [[ -n "$ADDRESS" ]] || { echo "could not read the bridge address from $PARAMS"; exit 1; }
 echo "bridge up at $ADDRESS"
 
-# 🔴 `--rerun-tasks`, because Gradle's up-to-date check does not know the
+# `--rerun-tasks`, because Gradle's up-to-date check does not know the
 # counterparty changed. Without it a second run skips the task entirely and
-# prints nothing — the tests do not fail, they simply never happen. Caught by
+# prints nothing, the tests do not fail, they simply never happen. Caught by
 # the name check below, which is the second time that check has earned its keep
 # in ten minutes.
 OBFS4_INTEROP_PARAMS="$PARAMS" OBFS4_INTEROP_CLIENT="$WORK/interopclient" \
     ./gradlew :obfs4:test --tests '*InteropTest*' --rerun-tasks --console=plain 2>&1 \
     | tee "$WORK/test.log"
 
-# 🔴 A Gradle filter that matches nothing still exits 0, which would make "no
+# A Gradle filter that matches nothing still exits 0, which would make "no
 # interop coverage at all" look exactly like success.
 for name in "a handshake and an echo against a real lyrebird bridge" \
             "a bridge ignores a handshake it cannot verify" \
             "a real lyrebird client accepts the kotlin bridge"; do
-    # ⚠️ Gradle prints `name() PASSED`, with parentheses. Matching on
-    # "$name PASSED" silently matches nothing — which this check caught on
+    # Gradle prints `name() PASSED`, with parentheses. Matching on
+    # "$name PASSED" silently matches nothing, which this check caught on
     # itself, reporting failure while all three tests had passed.
     grep -qF "$name() PASSED" "$WORK/test.log" || {
         echo