feat: add alias creation to pos system bank interactive menu

New 'alias' subcommand (+ POS_SUBCMDS row, menu option 6 'Manage
aliases'): create/update/list/remove bash aliases that run
'pos system bank run <name>', written into ~/.bashrc inside a managed
marker block (BASH_RC_FILE seam for tests, atomic tmp+mv rewrite).

- alias_valid_name enforces ^[a-zA-Z][a-zA-Z0-9_-]*$
- same-name create is an idempotent retarget; last alias removal cleans
  the whole block; outer ~/.bashrc aliases preserved byte-identically
- outer-alias collision refused (file untouched), PATH-shadow non-blocking
  warn, 'bank remove' drops aliases pointing at the removed command
- GNU sed '1,0p' edge case (block at line 1) fixed with guarded ranges;
  regex-quote literalization avoided via glob case payload match
- t-bank.sh +49 checks (71 -> 120); docs: POS.md, howto/system.md,
  tests/README.md, AGENT_TODO.md; make gen byte-idempotent
  (also refreshes the pos-communication-telegram-listener filetable
  line count so the previous commit's tree is gen-consistent)

DOC/howto/system.md

@@ -1,7 +1,8 @@
 # How-To: `pos system`
 
-Host care: encrypted backups, firewall, health dashboard, and uninstall. Tools:
-`backup`, `firewall`, `health`, `uninstall`.
+Host care: encrypted backups, firewall, health dashboard, uninstall, and the
+persistent command bank. Tools: `backup`, `firewall`, `health`, `uninstall`,
+`bank`.
 
 | Tool | What it does |
 |------|--------------|
@@ -9,6 +10,7 @@ Host care: encrypted backups, firewall, health dashboard, and uninstall. Tools:
 | `pos system backup` | gpg-encrypted (AES-256) folder snapshots |
 | `pos system firewall` | Interactive UFW ("UFW POWER") management |
 | `pos system uninstall` | Safe, interactive uninstaller for the pos toolkit |
+| `pos system bank` | Persistent command bank — save, run, and alias shell commands |
 
 ---
 
@@ -233,6 +235,39 @@ confirmation. The git repo is **never** removed — delete it manually if desire
 - "Nothing to remove" → pos toolkit is not installed (or already removed)
 - After uninstall, run `source ~/.bashrc` or restart your shell
 
+## `pos system bank` — persistent command bank + bash aliases
+
+```bash
+pos system bank add convert "Convert video" "ffmpeg -i {input} -crf {quality} {output}"
+pos system bank list
+pos system bank run convert input=clip.mp4 quality=23 output=clip.mkv
+pos system bank alias convert conv    # bash alias: conv='pos system bank run convert'
+pos system bank alias list
+```
+
+The bank is a persistent store of shell commands in
+`~/.config/linux_post_install/bank.env` (pipe-delimited, chmod 600, managed by
+the tool). `{param}` placeholders are substituted at run time; on a TTY with no
+arguments the tool opens an interactive menu.
+
+**Bash aliases** are written to `~/.bashrc` inside a managed block
+(`# >>> pos bank aliases … <<<`), one line per alias:
+`alias <alias_name>='pos system bank run <name>'`. Details:
+
+- Default alias name is the bank name; pass a second argument for a shorter one:
+  `pos system bank alias convert conv`.
+- Reusing an alias name **retargets** it to the new bank command; removing the
+  last alias removes the whole managed block.
+- An alias name already defined elsewhere in `~/.bashrc` is **refused** (shown
+  with its line) so the managed block never shadows your own config. Aliasing a
+  command that also exists on `PATH` prints a non-blocking notice that it will
+  shadow the real command in interactive shells.
+- `pos system bank remove <name>` also drops aliases pointing at the removed
+  command.
+
+After adding/removing an alias, run `source ~/.bashrc` (or open a new shell)
+for it to take effect.
+
 ---
 
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