fix: stop pointing agents at CLAUDE.md; AGENTS.md is the source of truth

[Patel230]

Makes AGENTS.md the single source of truth in rho's own guidance.

Changes

Site	Before	After
internal/engine/adaptive_system_prompt.go	"conventions documented in AGENTS.md and CLAUDE.md"	AGENTS.md only
internal/autoinit/autoinit.go	gate list included CLAUDE.md	AGENTS.md, RHO.md, CONTEXT.md
cmd/autoinit.go, autoinit doc comments	mentioned CLAUDE.md	updated
cmd/context_export.go	{"AGENTS.md", "AGENTS.md", "CLAUDE.md", ".rho.md"}	{"AGENTS.md", ".rho.md"}

Drive-by bug fix

cmd/context_export.go listed AGENTS.md twice, so the exporter read the same file and emitted a duplicate ## Project Instructions (AGENTS.md) section. Fixed as part of trimming that list.

Deliberately NOT changed

internal/rules/ (FormatClaudeCode, readClaudeCode/writeClaudeCode) and config.loadCrossAgentInstructions stay as they are. That is interop, not rho's own config — it lets people migrating in from Claude Code, Cursor, Copilot and Gemini keep their existing rules. Removing it would delete a migration feature.

Verification

go build ./... clean, gofumpt -l clean, tests pass across internal/autoinit, internal/config, internal/rules, internal/engine/..., cmd/....

🤖 Generated with Claude Code