Dev-only per-agent Skills panel (agent-skills step 4)

[yikkuro]

Summary

STEP 4 of the agent↔skills feature: a DEV-ONLY per-agent "Skills" panel so developers can toggle each agent's skill set at runtime and reload the gateway once — no code edits required.

The Skills tab and panel are gated on import.meta.env.DEV, so they are completely absent from production builds (import.meta.env.DEV is statically replaced with false and the v-if="isDev" gate keeps the button/panel out of the release DOM).

Stacking

This PR is stacked on:

• Bind per-agent skills into openclaw.json (step 2) #141 — sunt-microsoft-feat-agent-skills-binding-step2 (base of this PR)
• Add per-agent skills binding (step 1: data model, all agents default to all skills) #140 — step 1

Review/merge #140 and #141 first.

What changed

• ChatView: extend the viewMode union with "skills"; add a third mode-toggle-bar button (v-if="isDev", right of Chat/Studio) and render SkillsDevPanel when selected.
• SkillsDevPanel (new): agent picker (catalog agents), 23 skill toggles reflecting config.agents.list[<id>].skills, select-all / clear-all, and an Apply & reload button with applying/applied/failed feedback. Defaults to the current chat agent, else main.
• main.ts: new skills:set-agent-skills IPC — validates the agent id and that every skill id ∈ ALL_SKILL_IDS, writes openclaw.json atomically, and restarts the gateway once (with rollback on failure). Exposed via preload as window.openclaw.skills.setAgentSkills.
• agent-catalog: add pure isKnownSkillId / sanitizeAgentSkillIds helpers.
• agent-personas (step-2 seeding change): ensureAgentPersonasConfig now seeds a catalog agent's skills fill-if-missing (only when the entry has no skills key) instead of authoritatively overwriting every gateway boot. This prevents the boot seeding from wiping dev toggles when the gateway reloads to apply them. Fresh installs still get the full catalog list seeded via createAgentEntry; only the "heal stale values every boot" behavior is dropped, which is safe for release (no Skills UI ships to users).
• i18n: add skills.dev.* keys in both en-US and zh-CN.

Validation (from desktop/)

• npm test (main): 679 passed
• npm test (renderer): 198 passed
• npx tsc --noEmit: clean
• npx vue-tsc --noEmit (renderer): clean
• npx vite build (renderer): succeeds; import.meta.env.DEV → 0 unreplaced occurrences, so the dev button/panel are inert in prod
• ESLint on changed files: no new issues (only pre-existing warnings + the known main.ts preserve-caught-error remain)

Manual test

1. npm run dev in desktop/.
2. A Skills button appears next to Chat/Studio.
3. Pick an agent, toggle some skills, click Apply & reload.
4. The gateway comes back and config.agents.list[<agent>].skills reflects the change — and the change survives the reload (fill-if-missing seeding no longer overwrites it).
5. Build a release (vite build) and confirm the Skills button is not present.