feat(mcp): token budget management with progressive disclosure

[prosdev]

Summary

Implements #71 - Token budget management for search results (sub-issue 5/5 of Epic #66)

Changes

New Parameters

• Added tokenBudget parameter to dev_search tool (500-10000 tokens)
  • Compact mode default: 2000 tokens
  • Verbose mode default: 5000 tokens

Progressive Disclosure Strategy

• Full detail (top 3 results): Complete snippet + imports + metadata
• Signature detail (next 4 results): Signature + metadata (no snippet body)
• Minimal detail (remaining): Header + location only
• Truncation notice when budget exceeded

Formatter Options

Added to FormatterOptions:

• progressiveDisclosure: Enable/disable (default: true)
• fullDetailCount: Top N results with full detail (default: 3)
• signatureDetailCount: Next M results with signatures (default: 4)
• DetailLevel type: 'full' | 'signature' | 'minimal'

Token Estimation

Improved estimateTokensForText() with:

• estimateCodeRatio() for code-heavy text detection
• More accurate token estimation (3.5 chars/token for code vs 4 chars/token for prose)

Testing

• 10 new tests for token budget management
• All 1292 tests passing

Example Output

With budget of 2000 tokens and 10 results:

# Search Results (10 found, showing 7 within budget)

## 1. createPlan (function) - packages/subagents/src/planner/planner.ts
[Full snippet + imports + metadata]

## 2. handleMessage (method) - packages/subagents/src/planner/planner.ts
[Full snippet + imports + metadata]

## 3. PlannerAgent (class) - packages/subagents/src/planner/planner.ts
[Full snippet + imports + metadata]

## 4. breakdownTasks (function) - packages/subagents/src/planner/utils/breakdown.ts
[Signature only + metadata]

## 5. estimateEffort (function) - packages/subagents/src/planner/utils/estimation.ts
[Signature only + metadata]

...

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*3 more results (token budget reached)*

Closes #71