feat: custom prefix + SKILL_NAME templating — /g-ship, /g-qa in one command (v0.12.12.0)

[lucaslim]

Summary

• Custom prefix word. Setup now offers 3 choices: short names (`/qa`), namespaced (`/gstack-qa`), or a custom word you type (`g`, `gs`, `mytools`). The dash separator is automatic.
• `{{SKILL_NAME}}` template variable. SKILL.md templates now use `name: {{SKILL_NAME}}` in frontmatter. The generator resolves this to the prefixed name at build time (e.g. `name: g-ship` when prefix is `g`). Claude Code uses the `name:` field as the slash command trigger — this is what makes `/g-ship` actually work, not just a renamed directory.
• Live reload. `gstack-config set skill_prefix g` regenerates all installed SKILL.md files immediately — no setup re-run needed.
• `--prefix ` flag. Takes a word argument now (`--prefix g`) instead of being a toggle. `--no-prefix` unchanged.
• Universal cleanup. Any prefix → any prefix cleans up old generated dirs first, using `AUTO-GENERATED from SKILL.md.tmpl` as the detection signal.

What changed

File	Change
`bin/gstack-config`	Validation, empty string handling, backward compat (`true`→`gstack`), live regen trigger, `readlink -f` path resolution, `
`setup`	`SKILL_PREFIX` is now a string word; 3-option interactive prompt; `validate_prefix()`; `cleanup_generated_skill_dirs()` replaces 2 old cleanup functions; `GSTACK_SKIP_REGEN=1` prevents double regen
`scripts/gen-skill-docs.ts`	`{{SKILL_NAME}}` resolution from dir name + prefix; `--output-root ` for installing to target dir without modifying source
`scripts/resolvers/preamble.ts`	Updated prefix instruction — handles arbitrary word, not just legacy `"true"`
29 SKILL.md + templates	`name: {{SKILL_NAME}}` in all templates; regenerated with updated preamble text
`test/gen-skill-docs.test.ts`	8 updated tests for string-based prefix, universal cleanup, 3-option prompt

How the name templating works

Every SKILL.md template has `name: {{SKILL_NAME}}` in its frontmatter. When `gen-skill-docs.ts` runs:

1. It derives the base name from the directory (`ship`, `qa`, etc.)
2. If a prefix is set (e.g. `g-`), it prepends it: `g-ship`
3. The generated `SKILL.md` gets `name: g-ship`
4. Claude Code reads that `name:` field and registers `/g-ship` as the trigger

Without this, renaming the directory to `g-ship/` would create the file path but Claude Code would still look for a different name. The `name:` field is the actual hook.

Test plan

• `bun test` — 591 pass, 0 fail
• `{{SKILL_NAME}}` resolves correctly with and without prefix (gen-skill-docs tests)
• `gstack-config get skill_prefix` returns `gstack` when stored value is `true` (backward compat)
• `gstack-config set skill_prefix g` validates format and triggers regen
• Setup 3-option prompt tested (choice 1/2/3, custom word input, validation)
• Universal cleanup detects by `AUTO-GENERATED` header, not prefix string
• `GSTACK_SKIP_REGEN=1` suppresses double regen when called from setup
• PATH-invoked `gstack-config` resolves gstack dir via `readlink -f`

Design doc

APPROVED by autoplan (CEO + Eng reviews): `~/.gstack/projects/lucaslim-gstack/lucaslim-lucaslim-skill-prefix-frontmatter-sync-design-20260327-131400.md`

9 MUST-FIX items from eng review — all addressed before coding began.