chore: minor fixes from final review (Dockerfile reproducibility, Caddy directive, em dash)

M3: frontend/Dockerfile now copies package-lock.json and uses npm ci instead
of npm install, for reproducible builds.

M4: replace em dash with plain hyphen in manual_share.py's attachment-only
fallback text (standing style preference; ping.py title and
TriageList.vue's sender fallback were already fixed in prior commits).

M5: Caddyfile.snippet uses basic_auth instead of the deprecated basicauth
directive alias (Caddy 2.8+).

M1/M2/M6 (unused discord import removal, None-payload guard in
_extract_body, discord.NotFound guard in thread_ingest.py) were already
included in the preceding two commits since they touched the same files.

Caddyfile.snippet

@@ -1,5 +1,5 @@
 chorus.circuitforge.tech {
-    basicauth {
+    basic_auth {
         donna <bcrypt-hash-here>
         alan <bcrypt-hash-here>
     }

bot/chorus_bot/cogs/manual_share.py

@@ -23,7 +23,7 @@ class ManualShareCog(commands.Cog):
             return
 
         raw_content = message.content
-        display_content = message.content or "(attachment only — see original message)"
+        display_content = message.content or "(attachment only - see original message)"
         snippet = display_content if len(display_content) <= 120 else display_content[:117] + "..."
 
         embed = build_ping_embed(

frontend/Dockerfile

@@ -1,7 +1,7 @@
 FROM node:20-slim AS build
 WORKDIR /app
-COPY package.json .
-RUN npm install
+COPY package.json package-lock.json .
+RUN npm ci
 COPY . .
 RUN npm run build