feat(v0.3): add built-in project CLAUDE.md template

ClaudeMDProject returns the project-oriented default used when
--project is passed (and no project seed overrides it). Adds tests
asserting required v0.3 spec sections and ASCII-only content.

internal/seed/templates.go

@@ -39,6 +39,40 @@ Keep it concise -- a few bullet points is enough.
 `
 }
 
+// ClaudeMDProject returns the built-in default CLAUDE.md content for a project workspace.
+func ClaudeMDProject() string {
+	return `# Project Workspace Guidelines
+
+This is a ctask project workspace -- a long-lived working environment, not a disposable task.
+
+## File Placement
+
+- Source code -> ` + "`src/`" + ` or workspace root
+- Documentation -> ` + "`docs/`" + `
+- Deliverables and exports -> ` + "`output/`" + `
+- Reference material -> ` + "`context/`" + `
+- Tests -> ` + "`tests/`" + `
+- Configuration files -> workspace root
+- Do not place non-code outputs in the workspace root
+
+## Conventions
+
+- This project uses git. Commit meaningful changes with clear messages.
+- Do not install global packages or modify system files unless asked.
+- Record important assumptions and actions in notes.md.
+- Keep the workspace root clean.
+
+## Session Handoff
+
+Before ending a session, append a brief summary to notes.md with:
+
+- What was accomplished
+- Key decisions made
+- Open follow-ups or unfinished work
+- How to continue from here
+`
+}
+
 // NotesMD returns the skeleton notes.md content.
 func NotesMD(title string) string {
 	return fmt.Sprintf(`# %s