feat(#778): cross-runtime command enrichment (Gemini {{args}}/!{}, Qwen priority) (#825)

* feat(#778): cross-runtime command enrichment (Gemini {{args}}/!{}, Qwen priority)

Enrich the installer's per-runtime command/skill generators with native,
verified, additive fields:

- Gemini CLI: map Claude's $ARGUMENTS -> Gemini's {{args}} in generated TOML
  commands so typed arguments interpolate; inject live .planning/STATE.md into
  /gsd:progress via a fixed, injection-safe !{cat .planning/STATE.md 2>/dev/null}
  shell block (no interpolated input).
- Qwen Code: emit the optional numeric `priority` field on main-loop skills so
  the most-used workflows sort first in the /skills list (higher = earlier per
  the Qwen skills spec; the issue's inverse numbering was corrected).

OpenCode per-command model/agent/subtask/variant enrichment was evaluated and
intentionally not implemented: `model` reintroduces the #1156
ProviderModelNotFoundError regression for non-Anthropic providers (the converter
deliberately strips model:), `subtask`/`agent` change execution semantics for
GSD's interactive commands, and `variant` is not in the OpenCode command schema.

Schemas verified against primary docs (Gemini custom-commands, Qwen skills,
OpenCode commands/skills). Adds tests/enh-778-* and how-to + USER-GUIDE docs.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* chore(#778): set changeset PR number to 825

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

docs/how-to/install-on-your-runtime.md

@@ -96,6 +96,11 @@ npx @opengsd/gsd-core@latest --gemini --global
 
 Skills land in `~/.gemini/`. The installer rewrites all command bodies to Gemini's colon namespace (`/gsd:update`, `/gsd:config`, etc.). Restart Gemini CLI after install.
 
+The installer also enriches the generated TOML commands with two native Gemini custom-command features:
+
+- **`{{args}}` interpolation** — every command that references arguments inline is emitted with Gemini's `{{args}}` placeholder (translated from Claude's `$ARGUMENTS`), so flags and free-text you type after the command name are interpolated into the prompt body rather than ignored.
+- **`!{...}` live-state injection** — `/gsd:progress` injects the current contents of `.planning/STATE.md` via a fixed `!{cat .planning/STATE.md 2>/dev/null}` shell block, giving Gemini live project state without relying on session memory. The shell block contains no interpolated input, so there is no injection risk; Gemini still shows its standard confirmation dialog the first time the command runs in a session.
+
 **Override the install directory:**
 
 ```bash
@@ -290,6 +295,8 @@ npx @opengsd/gsd-core@latest --qwen --global
 
 Skills land in `~/.qwen/skills/gsd-*/SKILL.md`.
 
+GSD's main-loop skills are emitted with Qwen's optional numeric `priority` frontmatter field so the most-used workflows surface first in the `/skills` TUI list. Higher values sort earlier (per Qwen's skills spec), so core commands such as `/skills` for `new-project` (100), `plan-phase` (90), and `execute-phase` (85) appear above utility skills, which are left unset (default 0). This affects only the `/skills` list order — slash-command completion and `/help` remain alphabetical.
+
 **Override the install directory:**
 
 ```bash