feat(skills): /learn — distill a reusable skill from anything you describe (#51506)

Open-ended skill learning across every surface. /learn <free text> takes a
description of any source — a directory, a URL, the workflow you just walked
the agent through, or pasted notes — and the live agent gathers it with the
tools it already has (read_file/search_files, web_extract, the conversation,
the pasted text), then authors a SKILL.md via skill_manage following the
house authoring standards (<=60-char description, the standard section order,
Hermes-tool framing, no invented commands).

No engine, no model-tool footprint, works on any terminal backend (local,
Docker, remote): /learn builds a standards-guided prompt and hands it to the
agent as a normal turn.

- agent/learn_prompt.py: shared standards-guided prompt builder
- /learn registry entry (both surfaces) + CLI handler (inject onto input
  queue) + gateway handler (rewrite turn, fall through, /blueprint pattern)
- tui_gateway command.dispatch returns a send directive -> TUI + dashboard chat
- dashboard Skills page 'Learn a skill' panel (dir + URL + open-ended text)
  composes a /learn request and runs it in chat
- docs (slash-commands ref + skills feature page), 11 targeted tests

Inspired by OpenAI Codex's Record & Replay and the /learn concept from #47234
(dir-distillation engine); reworked to be open-ended and engine-free per
review.

website/docs/reference/slash-commands.md

@@ -89,6 +89,7 @@ Type `/` in the CLI to open the autocomplete menu. Built-in commands are case-in
 | `/skills` | Search, install, inspect, or manage skills from online registries. Also the review surface for the skill write-approval gate: `/skills pending`, `/skills diff <id>`, `/skills approve <id>`, `/skills reject <id>`, `/skills approval on\|off`. See [Gating agent skill writes](/user-guide/features/skills#gating-agent-skill-writes-skillswrite_approval). |
 | `/memory [pending\|approve\|reject\|approval]` | Review pending memory writes staged by the write-approval gate (`memory.write_approval`) and toggle the gate. See [Controlling memory writes](/user-guide/features/memory#controlling-memory-writes-write_approval). |
 | `/bundles` | List configured skill bundles — `/<name>` slash aliases that preload several skills at once. Configure under `bundles:` in `~/.hermes/config.yaml`. See [Skill Bundles](/user-guide/features/skills#skill-bundles). |
+| `/learn <what to learn from>` | Distill a reusable skill from anything you describe — a directory, a URL, the workflow you just walked the agent through, or pasted notes. Open-ended: the agent gathers the sources with its own tools and authors a `SKILL.md` following the house authoring standards. Works in the CLI, the messaging gateway, the TUI, and the dashboard Skills page. |
 | `/cron` | Manage scheduled tasks (list, add/create, edit, pause, resume, run, remove) |
 | `/suggestions [accept\|dismiss N\|catalog\|clear]` (alias: `/suggest`) | Review suggested automations. Use `/suggestions` to list pending suggestions, `/suggestions accept <id>` to create the proposed automation, `/suggestions dismiss <id>` to reject one, `/suggestions catalog` to add curated starter automations, and `/suggestions clear` to clear resolved suggestion records. Accepted jobs preserve the current surface as the delivery origin. |
 | `/blueprint [name] [slot=value ...]` (alias: `/bp`) | Set up an automation from a blueprint template. Bare `/blueprint` lists the catalog; `/blueprint <name>` starts a guided slot-filling flow on the next agent turn; `/blueprint <name> slot=value ...` creates the job directly. |
@@ -249,7 +250,7 @@ The messaging gateway supports the following built-in commands inside Telegram,
 - `/skills` is **CLI-only for search/browse/install**; its write-approval review subcommands (`pending`, `approve`, `reject`, `diff`, `approval`) also work on messaging platforms when `skills.write_approval` is on. `/memory` works on **both** surfaces.
 - `/verbose` is **CLI-only by default**, but can be enabled for messaging platforms by setting `display.tool_progress_command: true` in `config.yaml`. When enabled, it cycles the `display.tool_progress` mode and saves to config.
 - `/sethome`, `/update`, `/restart`, `/approve`, `/deny`, `/topic`, `/platform`, and `/commands` are **messaging-only** commands.
-- `/status`, `/version`, `/background`, `/queue`, `/steer`, `/voice`, `/reload-mcp`, `/reload-skills`, `/rollback`, `/debug`, `/fast`, `/footer`, `/curator`, `/kanban`, `/credits`, `/suggestions`, `/blueprint`, `/sessions`, and `/yolo` work in **both** the CLI and the messaging gateway.
+- `/status`, `/version`, `/background`, `/queue`, `/steer`, `/voice`, `/reload-mcp`, `/reload-skills`, `/rollback`, `/debug`, `/fast`, `/footer`, `/curator`, `/kanban`, `/credits`, `/suggestions`, `/blueprint`, `/learn`, `/sessions`, and `/yolo` work in **both** the CLI and the messaging gateway.
 - `/voice join`, `/voice channel`, and `/voice leave` are only meaningful on Discord.
 - In the TUI, `/sessions` shows live sessions in the current TUI process. Use `/resume [name]` or `hermes --tui --resume <id-or-title>` for saved or closed transcripts.