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.

completions/pos.bash

@@ -23,15 +23,16 @@ _pos_flags[share-usb-server]="--ls --ls-shared --share --unshare --auto-share --
 _pos_flags[system-backup]="--service --no-encrypt"
 _pos_flags[system-schedule]="--dry-run"
 _pos_flags[system-uninstall]="--yes --config --data"
-_pos_flags[ai]="--provider --model --session --system --full --last --trust"
+_pos_flags[ai]="--provider --model --session --system --full --last --trust --no-command-execution"
 _pos_flags[tree]="--depth"
 # GEN:END posflags
 # GEN:START possubcmds
 declare -A _pos_subcmds
 _pos_subcmds[ai-alias]="create edit remove list show"
-_pos_subcmds[ai-gemini]="ask chat models sessions capture"
-_pos_subcmds[ai-llamacpp]="ask chat models sessions capture"
-_pos_subcmds[ai-openrouter]="ask chat sessions capture"
+_pos_subcmds[ai-gemini]="ask chat models sessions capture providers"
+_pos_subcmds[ai-hf]="search download list remove info files cache"
+_pos_subcmds[ai-llamacpp]="ask chat models sessions capture providers"
+_pos_subcmds[ai-openrouter]="ask chat sessions capture models providers"
 _pos_subcmds[ai-server]="start stop status models logs"
 _pos_subcmds[communication-matrix-sender]="send test login"
 _pos_subcmds[communication-scrcpy]="devices record tcpip connect push pull screenshot info"
@@ -48,7 +49,7 @@ _pos_subcmds[share-smb-client]="mount unmount list persist unpersist menu"
 _pos_subcmds[share-smb-server]="status share unshare list adduser deluser reload enable disable menu"
 _pos_subcmds[system-backup]="menu"
 _pos_subcmds[system-schedule]="run list config enable disable status migrate menu"
-_pos_subcmds[ai]="ask chat sessions capture models providers alias gemini hf llamacpp openrouter server"
+_pos_subcmds[ai]="ask chat sessions capture models providers llamacpp alias gemini hf openrouter server"
 # GEN:END possubcmds
 # GEN:START posconfigscopes
 declare -a _pos_config_scopes=(ai compose entertainment grab matrix notify scrcpy system telegram ytsync)