mom: add centralized logging, usage tracking, and improve prompt caching

Major improvements to mom's logging and cost reporting:

Centralized Logging System:
- Add src/log.ts with type-safe logging functions
- Colored console output (green=user, yellow=mom, dim=details)
- Consistent format: [HH:MM:SS] [context] message
- Replace scattered console.log/error calls throughout codebase

Usage Tracking & Cost Reporting:
- Track tokens (input, output, cache read/write) and costs per run
- Display summary at end of each run in console and Slack thread
- Example: 💰 Usage: 12,543 in + 847 out (5,234 cache read) = $0.0234

Prompt Caching Optimization:
- Move recent messages from system prompt to user message
- System prompt now mostly static (only changes with memory files)
- Enables effective use of Anthropic's prompt caching
- Significantly reduces costs on subsequent requests

Model & Cost Improvements:
- Switch from Claude Opus 4.5 to Sonnet 4.5 (~40% cost reduction)
- Fix Claude Opus 4.5 cache pricing in ai package (was 3x too expensive)
- Add manual override in generate-models.ts until upstream fix merges
- Submitted PR to models.dev: https://github.com/sst/models.dev/pull/439

UI/UX Improvements:
- Extract actual text from tool results instead of JSON wrapper
- Cleaner Slack thread formatting with duration and labels
- Tool args formatting shows paths with offset:limit notation
- Add chalk for colored terminal output

Dependencies:
- Add chalk package for terminal colors

packages/ai/CHANGELOG.md

@@ -0,0 +1,15 @@
+# Changelog
+
+## [Unreleased]
+
+### Fixed
+
+- **Fixed Claude Opus 4.5 cache pricing** (was 3x too expensive)
+  - Corrected cache_read: $1.50 → $0.50 per MTok
+  - Corrected cache_write: $18.75 → $6.25 per MTok
+  - Added manual override in `scripts/generate-models.ts` until upstream fix is merged
+  - Submitted PR to models.dev: https://github.com/sst/models.dev/pull/439
+
+## [0.9.4] - 2025-11-26
+
+Initial release with multi-provider LLM support.

packages/ai/scripts/generate-models.ts

@@ -295,6 +295,14 @@ async function generateModels() {
 	// Combine models (models.dev has priority)
 	const allModels = [...modelsDevModels, ...openRouterModels];
 
+	// Fix incorrect cache pricing for Claude Opus 4.5 from models.dev
+	// models.dev has 3x the correct pricing (1.5/18.75 instead of 0.5/6.25)
+	const opus45 = allModels.find(m => m.provider === "anthropic" && m.id === "claude-opus-4-5");
+	if (opus45) {
+		opus45.cost.cacheRead = 0.5;
+		opus45.cost.cacheWrite = 6.25;
+	}
+
 	// Add missing gpt models
 	if (!allModels.some(m => m.provider === "openai" && m.id === "gpt-5-chat-latest")) {
 		allModels.push({

packages/ai/src/models.generated.ts

@@ -118,8 +118,8 @@ export const MODELS = {
 			cost: {
 				input: 5,
 				output: 25,
-				cacheRead: 1.5,
-				cacheWrite: 18.75,
+				cacheRead: 0.5,
+				cacheWrite: 6.25,
 			},
 			contextWindow: 200000,
 			maxTokens: 64000,