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/constants/skills.ts

@@ -0,0 +1,132 @@
+/**
+ * Skill System Constants
+ *
+ * Constants for skill loading, matching, and execution.
+ */
+
+import { join } from "path";
+import { DIRS } from "@constants/paths";
+
+/**
+ * Skill file configuration
+ */
+export const SKILL_FILE = {
+  NAME: "SKILL.md",
+  FRONTMATTER_DELIMITER: "---",
+  ENCODING: "utf-8",
+} as const;
+
+/**
+ * Skill directories
+ */
+export const SKILL_DIRS = {
+  BUILTIN: join(__dirname, "..", "skills"),
+  USER: join(DIRS.config, "skills"),
+  PROJECT: ".codetyper/skills",
+} as const;
+
+/**
+ * Skill loading configuration
+ */
+export const SKILL_LOADING = {
+  CACHE_TTL_MS: 60000,
+  MAX_SKILLS: 100,
+  MAX_FILE_SIZE_BYTES: 100000,
+} as const;
+
+/**
+ * Skill matching configuration
+ */
+export const SKILL_MATCHING = {
+  MIN_CONFIDENCE: 0.7,
+  EXACT_MATCH_BONUS: 0.3,
+  COMMAND_PREFIX: "/",
+  FUZZY_THRESHOLD: 0.6,
+} as const;
+
+/**
+ * Default skill metadata values
+ */
+export const SKILL_DEFAULTS = {
+  VERSION: "1.0.0",
+  TRIGGER_TYPE: "command" as const,
+  AUTO_TRIGGER: false,
+  REQUIRED_TOOLS: [] as string[],
+} as const;
+
+/**
+ * Skill error messages
+ */
+export const SKILL_ERRORS = {
+  NOT_FOUND: (id: string) => `Skill not found: ${id}`,
+  INVALID_FRONTMATTER: (file: string) => `Invalid frontmatter in: ${file}`,
+  MISSING_REQUIRED_FIELD: (field: string, file: string) =>
+    `Missing required field '${field}' in: ${file}`,
+  LOAD_FAILED: (file: string, error: string) =>
+    `Failed to load skill from ${file}: ${error}`,
+  NO_MATCH: "No matching skill found for input",
+  EXECUTION_FAILED: (id: string, error: string) =>
+    `Skill execution failed for ${id}: ${error}`,
+} as const;
+
+/**
+ * Skill titles for UI
+ */
+export const SKILL_TITLES = {
+  LOADING: (name: string) => `Loading skill: ${name}`,
+  EXECUTING: (name: string) => `Executing skill: ${name}`,
+  MATCHED: (name: string, confidence: number) =>
+    `Matched skill: ${name} (${(confidence * 100).toFixed(0)}%)`,
+  COMPLETED: (name: string) => `Skill completed: ${name}`,
+  FAILED: (name: string) => `Skill failed: ${name}`,
+} as const;
+
+/**
+ * Built-in skill IDs
+ */
+export const BUILTIN_SKILLS = {
+  COMMIT: "commit",
+  REVIEW_PR: "review-pr",
+  EXPLAIN: "explain",
+  FEATURE_DEV: "feature-dev",
+} as const;
+
+/**
+ * Skill trigger patterns for common commands
+ */
+export const SKILL_TRIGGER_PATTERNS = {
+  COMMIT: [
+    "/commit",
+    "commit changes",
+    "commit this",
+    "git commit",
+    "make a commit",
+  ],
+  REVIEW_PR: [
+    "/review-pr",
+    "/review",
+    "review pr",
+    "review this pr",
+    "review pull request",
+    "code review",
+  ],
+  EXPLAIN: [
+    "/explain",
+    "explain this",
+    "explain code",
+    "what does this do",
+    "how does this work",
+  ],
+  FEATURE_DEV: [
+    "/feature",
+    "/feature-dev",
+    "implement feature",
+    "new feature",
+    "build feature",
+  ],
+} as const;
+
+/**
+ * Required fields in skill frontmatter
+ */
+export const SKILL_REQUIRED_FIELDS = ["id", "name", "description", "triggers"] as const;