fix: MD5→SHA-256, shellcheck warnings, and broken doc links

config_service.py: replace MD5 with SHA-256 for config change detection;
same semantics (equality comparison), no stored hashes affected.

Shell scripts — shellcheck warnings:
- diagnose_web_interface.sh: remove useless cat (SC2002)
- dev_plugin_setup.sh: restructure A&&B||C into if/then (SC2015)
- fix_assets_permissions.sh: remove unused REAL_HOME block (SC2034)
- install_web_service.sh: remove unused USER_HOME assignment (SC2034)
- diagnose_web_ui.sh: remove unused SUDO assignments (SC2034)
- diagnose_plugin_permissions.sh: remove unused BLUE color var (SC2034)
- first_time_install.sh: remove unused CLEAR var, PACKAGE_NAME
  assignment, and replace loop variable with _ (SC2034)

docs/PLUGIN_ARCHITECTURE_SPEC.md: fix 10 broken TOC anchor links to
include section numbers matching the actual headings (MD051).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

first_time_install.sh

@@ -259,8 +259,6 @@ else
 fi
 
 echo ""
-CLEAR='
-'
 CURRENT_STEP="Install system dependencies"
 echo "Step 1: Installing system dependencies..."
 echo "----------------------------------------"
@@ -671,8 +669,6 @@ if [ -f "$PROJECT_ROOT_DIR/requirements.txt" ]; then
         echo "[$PACKAGE_NUM/$TOTAL_PACKAGES] Installing: $line"
         
         # Check if package is already installed (basic check - may not catch all cases)
-        PACKAGE_NAME=$(echo "$line" | sed -E 's/[<>=!].*$//' | sed 's/^[[:space:]]*//;s/[[:space:]]*$//')
-        
         # Try installing with verbose output and timeout (if available)
         # Use --no-cache-dir to avoid cache issues, --verbose for diagnostics
         INSTALL_OUTPUT=$(mktemp)
@@ -1479,7 +1475,7 @@ echo "WiFi Connection Status:"
 if command -v nmcli >/dev/null 2>&1; then
     WIFI_STATUS=$(nmcli -t -f DEVICE,TYPE,STATE device status 2>/dev/null | grep -i wifi || echo "")
     if [ -n "$WIFI_STATUS" ]; then
-        echo "$WIFI_STATUS" | while IFS=':' read -r device type state; do
+        echo "$WIFI_STATUS" | while IFS=':' read -r _ type state; do
             if [ "$state" = "connected" ]; then
                 SSID=$(nmcli -t -f active,ssid device wifi 2>/dev/null | grep "^yes:" | cut -d: -f2 | head -1)
                 if [ -n "$SSID" ]; then