delete the bug-report discord webhook, and the last dead HOME_DIR reads

DISCORD_BUG_REPORT_WEBHOOK is gone, with sendToDiscord and its helpers. Reports
still land in DATA_PATH/bug-reports — the disk write always happened first and
the webhook was only a ping about it, so nothing about the report is lost.

It was a personal notification channel living in deployment config, on a platform
whose owner is the only person who files reports. It was also never in
.env.example: the setup script wrote a variable nothing documented, which is the
same drift as PORT, in the other direction.

Note DISCORD_WEBHOOK_URL is a DIFFERENT variable — the notify sidecar's own
channel — and is untouched.

Then a parity sweep of setup / .env.example / what the code reads, which turned
up two leftovers from earlier today:

HOME_DIR was still read in six files, each with its own `?? homedir()` fallback.
Dead since nothing sets it, but a dead read is worse than none — it reads as a
supported override. They take homedir() directly now. user-instance.ts gets a
comment on why its line stays where it is: it sits above `process.env.HOME =
homeDir`, and homedir() reads $HOME, so a read moved below that assignment would
return whichever member was last spawned into. Two of the six had fallback chains
ending in process.cwd() and '' — the second would have silently disabled whatever
consumed it rather than failing.

VAULTWARDEN_URL was uncommented in .env.example among the variables setup writes,
though it is a plugin variable setup has never written. Commented out with the
other plugin entries.

The three files now agree: setup writes PORT, BROWSER_RELAY_PORT and
POSTGRES_URL; .env.example lists those plus JWT_SECRET and VAULT_STORE_KEY, which
are required by code and deliberately unwritten until the secret store lands.

Not typechecked (empty node_modules, frozen installs). Every changed file parses;
the setup section was run and writes three variables.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

scripts/setup/officer-setup.sh

@@ -460,7 +460,6 @@ if ! skip; then
 
   # Read back before anything is asked; existing values become the defaults.
   ENV_PORT="$(env_get PORT)"
-  ENV_DISCORD_WEBHOOK="$(env_get DISCORD_BUG_REPORT_WEBHOOK)"
   ENV_BROWSER_RELAY_PORT="$(env_get BROWSER_RELAY_PORT)"
 
   if env_exists; then