refactor: implement three-layer agent architecture (agents / prompts / skills)

Layer 1 — src/agents/ (thin agent definitions, no prompt text)
  registry.ts   — AgentConfig, registerAgent(), getAgent(), AGENTS proxy, pick()
  orchestrator.ts, coder.ts, pm.ts, marketing.ts — one file each, just metadata + tool picks
  index.ts      — barrel: imports prompts then agents (correct registration order)

Layer 2 — src/prompts/ (prompt text separated from agent logic)
  loader.ts     — registerPrompt(), resolvePrompt() with {{variable}} substitution
  orchestrator.ts, coder.ts, pm.ts, marketing.ts — prompt templates as registered strings
  orchestrator.ts now uses resolvePrompt('orchestrator', { knowledge }) instead of
  inline SYSTEM_PROMPT const; {{knowledge}} variable injects project memory cleanly.
  agent-runner.ts uses resolvePrompt(config.promptId) per agent turn.

Layer 3 — src/tools/skills.ts (new skills capability)
  list_skills(repo)      — lists .skills/<name>/SKILL.md directories from a Gitea repo
  get_skill(repo, name)  — reads and returns the markdown body of a skill file
  Orchestrator and all agents now have get_skill in their tool sets.
  Orchestrator also has list_skills and references skills in its prompt.

Also fixed:
  - server.ts now passes history + knowledge_context from request body to orchestratorChat()
    (these were being sent by the frontend but silently dropped)
  - server.ts imports PROTECTED_GITEA_REPOS from tools/security.ts (no more duplicate)
  - Deleted src/agents.ts (replaced by src/agents/ directory)

Made-with: Cursor

dist/prompts/loader.js

@@ -0,0 +1,30 @@
+"use strict";
+// ---------------------------------------------------------------------------
+// Prompt registry + variable resolver
+//
+// Prompts are template strings stored in this directory, one file per agent.
+// Variables are resolved at call time using {{variable_name}} syntax.
+//
+// Future: swap template strings for .md files with a build-time copy step.
+// ---------------------------------------------------------------------------
+Object.defineProperty(exports, "__esModule", { value: true });
+exports.registerPrompt = registerPrompt;
+exports.resolvePrompt = resolvePrompt;
+exports.hasPrompt = hasPrompt;
+const _prompts = new Map();
+function registerPrompt(id, template) {
+    _prompts.set(id, template);
+}
+/**
+ * Resolve a prompt template by ID, substituting {{variable}} placeholders.
+ * Missing variables are replaced with an empty string.
+ */
+function resolvePrompt(id, variables = {}) {
+    const template = _prompts.get(id);
+    if (!template)
+        throw new Error(`Prompt not found: "${id}"`);
+    return template.replace(/\{\{(\w+)\}\}/g, (_, key) => variables[key] ?? '');
+}
+function hasPrompt(id) {
+    return _prompts.has(id);
+}