docs: update website with implementation benchmark findings and v0.5.0 roadmap

[prosdev]

Summary

Major documentation update based on implementation benchmark findings. This PR supersedes #110.

Key Findings from Implementation Benchmarks

Task Type	Cost Savings	Time Savings
Debugging	42%	37%
Exploration	44%	19%
Implementation	29%	22%

Key insight: Savings scale with task complexity.

Why It Saves Money

What dev-agent does	Manual equivalent	Impact
Returns code snippets in search	Read entire files	99% fewer input tokens
dev_plan bundles issue + code + commits	5-10 separate tool calls	29% cost reduction
Semantic search finds relevant code	grep chains + filtering	42% cost reduction

Changes

Website (website/content/index.mdx)

• Highlight context bundling as core value prop
• Add "scales with complexity" messaging
• Show 99% input token reduction from code snippets
• Add dev_plan context bundling comparison (before/after tabs)
• Update benchmark results with task-type breakdown

Docs (website/content/docs/index.mdx)

• Add "Why it saves money" section
• Update benchmark data with task-type breakdown

PLAN.md

• Add v0.5.0 roadmap with dev_context generalization
• Add benchmark improvements for implementation task coverage
• Update benchmark results with token analysis

AGENTS.md & CLAUDE.md

• Update to show all 9 MCP tools (was missing dev_refs, dev_map, dev_history)
• Improve tool descriptions

Closes

This PR supersedes #110 (which only had the AGENTS.md/CLAUDE.md/PLAN.md updates). Please close #110 after merging this.