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

esbuild.config.js

@@ -1,7 +1,7 @@
 // @ts-check
 
 import { build } from "esbuild";
-import { mkdirSync, readFileSync, rmSync, writeFileSync } from "fs";
+import { cpSync, mkdirSync, readFileSync, rmSync, writeFileSync } from "fs";
 
 const pkg = JSON.parse(readFileSync("package.json", "utf-8"));
 
@@ -96,4 +96,9 @@ const cliPath = "./dist/cli.mjs";
 const cliContent = readFileSync(cliPath, "utf8");
 writeFileSync(cliPath, `#!/usr/bin/env node\n${cliContent}`);
 
+// copy bundled SKILL.md files into dist/ so the npm-published runtime can read
+// them via readFileSync. source-mode runs (PULLFROG_FORCE_LOCAL_CLI=1) read
+// directly from action/skills/ instead. see utils/skills.ts.
+cpSync("./skills", "./dist/skills", { recursive: true });
+
 console.log("» build completed successfully");