Remove internal-numbering / migration comments referencing invisible context

[sbryngelson]

Comments that reference an external/now-invisible context (a private "feature list" and a directory migration), which mean nothing to a reader of the public repo.

1. "Feature N" task-number comments in toolchain/mfc/viz/tui.py (10 occurrences):

87:  """Posted when the user clicks a heatmap cell (Feature 5)."""
126: # Zoom helpers (Feature 6)
153: # Mouse scroll handlers — zoom (Feature 6)
179: """Feature 5 — post Clicked message with the data value at the heatmap cell."""
269: # Apply zoom window to data index ranges (Feature 6).
278: # Cache for click/scroll coordinate mapping (Features 5 & 6).
517: # MFCPlot.Clicked handler — update status bar (Feature 5)
524: # Background data loading (Feature 4)
601: # Update step counter (Feature 2).
656: """Feature 6 — reset 2D zoom to full view."""

"Feature 2/4/5/6" reference an external/private feature checklist not in the repo. Strip the "(Feature N)" tags, keep the descriptive text.

2. Orphaned "Justification" comment — toolchain/mfc/case_validator.py:14

# Justification: Comprehensive validator covering all MFC parameter constraints

A dangling line after the module docstring; reads like a leftover review note. Remove or fold into the docstring.

3. Migration note — toolchain/mfc/params/definitions.py:1-6

Single file containing all ~3,300 parameter definitions using loops.
This replaces the definitions/ directory.

"This replaces the definitions/ directory" documents a past migration; that directory no longer exists, so the note refers to invisible history. Remove the migration sentence (keep the rest of the docstring).

---

_{Filed from a repo-wide code-cleanliness review; verified against master @ 40dde5e.}

Code references

• toolchain/mfc/viz/tui.py:87 — Feature N comment
• toolchain/mfc/case_validator.py:14 — orphaned Justification
• toolchain/mfc/params/definitions.py:1-6 — migration note