feat: command registry, alias wrapper scripts, config-ui readability

- lib/registry.sh: shared query API over POS_* headers (reg_scan, reg_list,
  reg_lookup, reg_tools_in, reg_each, reg_config_scopes/keys). Replaces
  per-consumer sed/grep header parsing.

- bin/pos-tree + bin/pos _pos_category_help(): migrated to registry API.
  Category help now shows [deps: ...] annotations. Tree output preserved.

- New optional headers # POS_DEPS: and # POS_EXAMPLES: in tool metadata.
  Added to pos-network-download (aria2c jq curl), pos-media-sync (lsblk jq),
  pos-system-backup (tar), pos-docker-ps (docker) as initial adopters.

- scripts/gen-docs.sh: extended tools array with deps/examples fields;
  conditional column rendering in gen_dispatch; deps annotation in gen_tree.
  Fixed URL-unsafe // joiner (→ middle dot ·) and \x1f caption delimiter
  collision in config-ui.

- bin/pos-ai-alias: rewrote activation from bash aliases (source-time-frozen)
  to executable wrapper scripts at ~/.local/bin. Staleness eliminated:
  edits apply on next invocation with no shell reload. _alias_sync()
  reconciliation on every subcommand, marker-guarded lifecycle, collision
  refusal, legacy .sh retirement. Fixed dup-table bug (option 4 no-op).

- lib/config-ui.sh: @caption/@[KEY=alt] conditional captions, *providers=<tag>
  tagged wildcards, uniform typography tier (bold/cyan/dim), honest prompt.
  Active provider keys bold, inactive dimmed with reason. Backward-compatible.

- bin/pos-system-uninstall: marker-scan for wrapper script cleanup.

- Docs synced: AGENTS.md (new headers + registry), DOC/SCRIPTS.md (registry
  section + lib list), DOC/POS.md (alias wrapper activation), MAINTENANCE.md
  (M-024). Lint fixed: pos-ai-alias registered in INTERACTIVE_CMDS.

Gates: make gen && make check && make lint = 0 FAIL, 0 WARN

bin/pos-tree

@@ -4,6 +4,7 @@ set -euo pipefail
 # POS_FLAGS: --depth
 
 source "$(dirname "$0")/../lib/common.sh" 2>/dev/null || source "$(dirname "$0")/common.sh"
+source "$(dirname "$0")/../lib/registry.sh" 2>/dev/null || source "$(dirname "$0")/registry.sh"
 
 usage() {
     cat <<EOF
@@ -44,12 +45,17 @@ add() {
     meta["$path"]="$type|$desc"
 }
 
-for f in "$self"/pos-*; do
-    [ -x "$f" ] || continue
-    name="${f##*/pos-}"
-    desc="$(sed -n '/^# POS: /{s/^# POS: //;p;q}' "$f")"
-    desc="${desc#*— }"
-    sc="$(sed -n '/^# POS_SUBCMDS: /{s/^# POS_SUBCMDS: //;p;q}' "$f")"
+reg_scan "$self"
+
+for tool_key in $(reg_list); do
+    cat="$(reg_lookup "$tool_key" cat)"
+    desc="$(reg_lookup "$tool_key" desc)"
+    sc="$(reg_lookup "$tool_key" subcmds)"
+    deps="$(reg_lookup "$tool_key" deps)"
+    name="${tool_key}"
+    if [ -n "$deps" ]; then
+        desc="$desc [deps: $deps]"
+    fi
     words=(${name//-/ })
     parent="/"
     for ((i=0; i<${#words[@]}; i++)); do