Respect ambiguous platform detection in resolveProjectPlatform instead of defaulting to claude-code

[LarsCowe]

Title: Respect ambiguous platform detection in resolveProjectPlatform instead of defaulting to claude-code

Summary

resolveProjectPlatform() still defaults to claude-code when bmalph/config.json is missing and platform detection is ambiguous. detectPlatform() now reports ambiguous root-only markers correctly, but that signal is discarded by the resolver fallback.

Current behavior

In configless projects:

• .cursor/ correctly resolves to cursor
• root-only AGENTS.md is treated by detection as ambiguous between codex and cursor
• root-only CLAUDE.md is treated by detection as ambiguous between claude-code and cursor
• but resolveProjectPlatform() still returns claude-code whenever detection.detected is null

Relevant code:

• src/platform/detect.ts
• src/platform/resolve.ts

Why this matters

This does not block the normal bmalph init --platform cursor -> implement -> run flow because initialized projects have explicit config. It does leave configless edge cases misaligned with the intended Cursor/Codex/Claude detection contract and can produce misleading status/doctor guidance.

Expected behavior

When config is missing and detection is ambiguous, the resolver should not silently default to claude-code.

Possible directions:

• return an explicit ambiguity result from the resolver and make callers handle it
• or raise a targeted error/warning telling the user to set the platform explicitly
• but do not collapse ambiguous detection into claude-code

Acceptance criteria

• resolveProjectPlatform() does not silently resolve ambiguous root-only markers to claude-code
• AGENTS.md-only projects are not treated as claude-code
• CLAUDE.md-only projects are not treated as claude-code unless there is an unambiguous Claude marker
• caller-facing commands (status, doctor, any other resolver consumers) produce explicit guidance for ambiguous detection paths
• tests cover the ambiguous detection + resolver behavior end to end