Add BRAIN_DISABLED flag and fix Ollama tool call formatting

Features:
  - Add BRAIN_DISABLED feature flag to hide all Brain functionality
  - When enabled, hides Brain banner, status indicator, menu, and commands
  - Flag location: src/constants/brain.ts

  Fixes:
  - Fix Ollama 400 error by properly formatting tool_calls in messages
  - Update OllamaMessage type to include tool_calls field
  - Fix Brain menu keyboard not working (add missing modes to isMenuOpen)

  UI Changes:
  - Remove "^Tab toggle mode" hint from status bar
  - Remove "ctrl+t to hide todos" hint from status bar

  Files modified:
  - src/constants/brain.ts (add BRAIN_DISABLED flag)
  - src/types/ollama.ts (add tool_calls to OllamaMessage)
  - src/providers/ollama/chat.ts (format tool_calls in messages)
  - src/tui-solid/components/header.tsx (hide Brain UI when disabled)
  - src/tui-solid/components/status-bar.tsx (remove hints)
  - src/tui-solid/components/command-menu.tsx (filter brain command)
  - src/tui-solid/components/input-area.tsx (fix isMenuOpen modes)
  - src/tui-solid/routes/session.tsx (skip brain menu when disabled)
  - src/services/brain.ts (early return when disabled)
  - src/services/chat-tui/initialize.ts (skip brain init when disabled)

src/types/skills.ts

@@ -0,0 +1,127 @@
+/**
+ * Skill System Types
+ *
+ * Types for the progressive disclosure skill system.
+ * Skills are loaded in 3 levels: metadata → body → external references.
+ */
+
+/**
+ * Skill loading level for progressive disclosure
+ */
+export type SkillLoadLevel = "metadata" | "body" | "full";
+
+/**
+ * Skill trigger types
+ */
+export type SkillTriggerType =
+  | "command"      // /commit, /review
+  | "pattern"      // "commit changes", "review PR"
+  | "auto"         // Automatically triggered based on context
+  | "explicit";    // Only when explicitly invoked
+
+/**
+ * Example for a skill
+ */
+export interface SkillExample {
+  input: string;
+  output: string;
+  description?: string;
+}
+
+/**
+ * Skill metadata (Level 1 - always loaded)
+ */
+export interface SkillMetadata {
+  id: string;
+  name: string;
+  description: string;
+  version: string;
+  triggers: string[];
+  triggerType: SkillTriggerType;
+  autoTrigger: boolean;
+  requiredTools: string[];
+  tags?: string[];
+}
+
+/**
+ * Skill body content (Level 2 - loaded on match)
+ */
+export interface SkillBody {
+  systemPrompt: string;
+  instructions: string;
+  templates?: Record<string, string>;
+}
+
+/**
+ * Full skill definition (Level 3 - loaded on execution)
+ */
+export interface SkillDefinition extends SkillMetadata, SkillBody {
+  examples?: SkillExample[];
+  externalRefs?: string[];
+  loadedAt?: number;
+}
+
+/**
+ * Skill match result from registry
+ */
+export interface SkillMatch {
+  skill: SkillDefinition;
+  confidence: number;
+  matchedTrigger: string;
+  matchType: SkillTriggerType;
+}
+
+/**
+ * Skill execution context
+ */
+export interface SkillContext {
+  sessionId: string;
+  workingDir: string;
+  gitBranch?: string;
+  userInput: string;
+  additionalContext?: Record<string, unknown>;
+}
+
+/**
+ * Skill execution result
+ */
+export interface SkillExecutionResult {
+  success: boolean;
+  skillId: string;
+  prompt: string;
+  error?: string;
+}
+
+/**
+ * Skill registry state
+ */
+export interface SkillRegistryState {
+  skills: Map<string, SkillDefinition>;
+  lastLoadedAt: number | null;
+  loadErrors: string[];
+}
+
+/**
+ * SKILL.md frontmatter parsed structure
+ */
+export interface SkillFrontmatter {
+  id: string;
+  name: string;
+  description: string;
+  version?: string;
+  triggers: string[];
+  triggerType?: SkillTriggerType;
+  autoTrigger?: boolean;
+  requiredTools?: string[];
+  tags?: string[];
+}
+
+/**
+ * Parsed SKILL.md file
+ */
+export interface ParsedSkillFile {
+  frontmatter: SkillFrontmatter;
+  body: string;
+  examples?: SkillExample[];
+  filePath: string;
+}