add bundled git-archaeology skill, auto-installed for opencode and claude (#565)

* add bundled git-archaeology skill, auto-installed for opencode and claude

ships a SKILL.md teaching agents the underused git history primitives
(pickaxe -S/-G, -L for function/line ranges, --reverse blame, deleted-file
recovery) so they stop scrolling git log -p when blame comes up empty.

introduces a lightweight bundled-skill path alongside the existing
addSkill (npx skills add) flow used for external skills like agent-browser.
SKILL.md is inlined into dist/cli.mjs via esbuild's text loader and written
to <home>/.agents/skills/<name>/SKILL.md at runtime — no network, no version
drift, no per-run install cost.

* fix: register vitest plugin to load .md as text for bundled-skill tests

* fix: drop vite type import from vitest plugin (vite isn't a direct dep)

* fix: load bundled skills via readFileSync so source mode works

esbuild's text loader only applies to the npm-bundled dist/cli.mjs path. the
preview / oss path runs cli.ts directly with node (PULLFROG_FORCE_LOCAL_CLI=1
in runCli.ts#runLocalCli), where node has no idea how to import .md files —
ERR_UNKNOWN_FILE_EXTENSION crashes the action before any agent starts.

switch to runtime readFileSync that checks both candidate locations:
- source mode: <actionRoot>/skills/<name>/SKILL.md (relative to utils/skills.ts)
- bundled mode: <distDir>/skills/<name>/SKILL.md (esbuild copies the tree)

drops the no-longer-needed esbuild text loader, vitest .md plugin, and
ambient *.md type declaration. wiki/skills.md updated with the why.

* fix: write bundled skills to per-agent dirs so claude actually registers them

agents/opencode.ts

@@ -21,7 +21,7 @@ import { getIdleMs, markActivity } from "../utils/activity.ts";
 import { log } from "../utils/cli.ts";
 import { installFromNpmTarball } from "../utils/install.ts";
 import { detectProviderError } from "../utils/providerErrors.ts";
-import { addSkill } from "../utils/skills.ts";
+import { addSkill, installBundledSkills } from "../utils/skills.ts";
 import { SPAWN_ACTIVITY_TIMEOUT_CODE, SpawnTimeoutError, spawn } from "../utils/subprocess.ts";
 import { ThinkingTimer } from "../utils/timer.ts";
 import type { TodoTracker } from "../utils/todoTracking.ts";
@@ -665,6 +665,8 @@ export const opencode = agent({
       agent: "opencode",
     });
 
+    installBundledSkills({ home: homeEnv.HOME });
+
     // base args shared between initial run and continue runs
     const baseArgs = ["run", "--format", "json", "--print-logs"];