fix: replace all non-ASCII characters with safe ASCII equivalents

Replace box-drawing characters (U+2500) in session log with ASCII dashes.
Replace em dashes (U+2014) in CLAUDE.md template with double hyphens.
Remove em dash from comment in run.go.
Add ASCII-guard tests for session log output and seed templates.
Prevents mojibake on Windows terminals that misinterpret UTF-8 as CP1252.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

internal/seed/templates.go

@@ -17,11 +17,11 @@ This workspace is scoped to a single task. Keep work focused on the task describ
 
 ## Files
 
-- task.yaml — Task metadata (machine-managed, do not edit)
-- notes.md — Task log (human/agent-managed)
-- context/ — Reference documents (user-managed)
-- output/ — Task deliverables and artifacts
-- logs/ — Session logs (automatic session snapshots)
+- task.yaml -- Task metadata (machine-managed, do not edit)
+- notes.md -- Task log (human/agent-managed)
+- context/ -- Reference documents (user-managed)
+- output/ -- Task deliverables and artifacts
+- logs/ -- Session logs (automatic session snapshots)
 
 ## Session Handoff
 
@@ -32,7 +32,7 @@ Before ending a session, append a brief summary to notes.md with:
 - Open follow-ups or unfinished work
 - How to continue from here
 
-Keep it concise — a few bullet points is enough. This helps the developer (or a future session) resume without losing context.
+Keep it concise -- a few bullet points is enough. This helps the developer (or a future session) resume without losing context.
 `, slug, category, workspacePath)
 }