fix: stabilization pass — fail-closed auth, ai flag validation, lint/config/security hardening, regression tests

17-point code-level audit executed via Explorer->Architect->Builder->Tester->Reviewer;
Reviewer accepted (APPROVE_WITH_NOTES; 3 block-list items resolved):

- security: telegram sender-owner AND-gate + TELEGRAM_OWNER_ID, matrix
  MATRIX_ROOM_ID fail-closed, gpg --passphrase-fd 3 (no argv secret),
  /dev/tcp positional-arg form (checkport/smb-client/share-lib/NET_PROBE),
  eval deny-by-default + --no-command-execution carried by both chat bridges,
  tty-gated --trust; config/{telegram,matrix}.env reference templates
- ai: all ExecStart flags validated against installed llama.cpp
  (requested->error, default->omit+warn, CONFIG_REQUESTED_FLAGS); single-file
  hf download failure rc=1 + no .hf-meta; LLAMACPP_HOST coherent;
  POS_SUBCMDS + metadata gaps closed
- tooling: lint-conventions Bash-native rewrite (~24-30x faster, rules and
  output byte-identical, :num restored); pos system uninstall covers all 12
  libs + scale-tail + flags dir + systemd user units (|| true) + plugin
  markers; anchored .bash_completion/.bashrc removal replaces sed -i '/pos/d'
- config: canonical load_env_file in lib/config-ui.sh (CRLF strip, env-wins,
  XDG, LOADED_ENV_KEYS); 9 tools migrated; entertainment-lib collapsed to
  wrappers; docker-compose deliberately unmigrated (source semantics)
- tests: first committed regression suite — tests/run-tests.sh zero-dep
  runner + make test; 12 files / 179 checks / 0 skip / ~52s; hard skip
  contract; systemd-analyze verify on generated unit PASS

Verified: make gen idempotent; make check green; make lint 0 FAIL, 0 WARN;
make test green; bash -n clean; git diff --check clean. Audit deliverables +
agent reports + AGENT_TODO Done entry included.

DOC/APPS.md

@@ -1,6 +1,6 @@
 # Optional Apps Reference
 
-`apps/` holds 15 optional desktop application installers, one script per app in `apps/<category>/<name>.sh`. They are **not** installed by the core bootstrap — run the picker explicitly.
+`apps/` holds 18 optional desktop application installers, one script per app in `apps/<category>/<name>.sh`. They are **not** installed by the core bootstrap — run the picker explicitly.
 
 - [The picker — `apps/install.sh`](#the-picker--appsinstallsh)
 - [How an app installer works](#how-an-app-installer-works)
@@ -34,7 +34,7 @@ bash apps/install.sh --uninstall brave   # uninstall a specific app
 
 ### Configuration
 
-- Categories: `browsers`, `development`, `media`, `networking`, `remote-access`, `system`, `utilities`.
+- Categories: `ai`, `browsers`, `development`, `media`, `networking`, `remote-access`, `system`, `utilities`.
 - Adding an app = dropping `apps/<category>/<name>.sh` into the folder. See [DEV.md](DEV.md) for the required installer conventions.
 
 ---
@@ -70,6 +70,7 @@ Installation methods used across the catalog:
 
 | App | Category | What it is | Install method |
 |-----|----------|------------|----------------|
+| llama.cpp | ai | Local LLM inference server (llama-server) | GitHub release → `/usr/local/lib/llama.cpp-<tag>` + `/usr/local/bin` symlinks |
 | Brave | browsers | Brave browser | apt repo + `apt install brave-browser` |
 | opencode | development | AI coding agent | official script → `~/.opencode/bin` |
 | VS Code | development | Code editor | Microsoft apt repo + `apt install code` |