feat: add text processing and content generation tools

[avoidwork]

Summary

Add dedicated text processing and content generation tools for copywriting, editing, SEO analysis, social media content, translation, and structured data extraction.

Motivation

The existing tools handle file extraction, web search, and image generation — but there is no dedicated capability for text processing and content generation. Marketing workflows specifically need: tone adjustment, summarization, rewriting, SEO analysis (keyword density, meta descriptions, SERP analysis), social media content generation (post scheduling, platform-specific formatting), translation, and text-to-structured-data (entity extraction, sentiment analysis). Currently the agent must rely on the LLM chain-of-thought without structured tooling, which is inconsistent and loses context.

Proposed Solution

Create a suite of text processing tools:

• Copywriting/Editing: Tone adjustment, summarization, rewriting, grammar correction, length adjustment (shorten/expand)
• SEO Analysis: Keyword density analysis, meta description generation, SERP analysis, content optimization suggestions
• Social Media Content: Platform-specific formatting (Twitter/X, LinkedIn, Instagram, TikTok), post scheduling, hashtag generation
• Translation: Multi-language translation with language detection
• Structured Data Extraction: Entity extraction, sentiment analysis, topic classification, key phrase extraction
• Text Comparison: Diff, similarity scoring, plagiarism detection

Each tool should follow the existing tool pattern in src/tools/ — a zod schema, an impl function, and registration in index.js.

Alternatives Considered

• Rely on LLM chain-of-thought: inconsistent output, no structured results, loses context across turns.
• Shell-based tools (sed, awk, python): fragile, requires user-installed dependencies, no NLP capabilities.

OpenSpec Note

This project uses OpenSpec for feature development. If this request is approved, I will:

1. Run /opsx:propose to generate a full proposal with specs and tasks
2. Iterate on the design before any code is written
3. Follow the task-driven implementation workflow

Additional Context

This should integrate with the document creation gap (#778) — e.g., generating marketing copy and then embedding it in a DOCX report. The existing webExtract tool could feed content into the text processing tools for analysis.