docs(6207): the remaining migrations state their rationale in terms of the data

Record, milestone, phase and plan citations go from every migration header;
the "end before start" fix (0043) and the suppressed-count column (0095)
state the condition they prevent rather than the incident. 0053 and 0055
pointed at design specs under docs/superpowers that are not in the repo;
those pointers are removed.

Kept: alembic's generated "Create Date:" headers (template metadata, not
rationale), 0121's ARM_BORN justification beside the constant, and 0051's
illustrative "update task 42" format example.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

alembic/versions/0054_drop_image_cache.py

@@ -4,7 +4,7 @@ Revision ID: 0054
 Revises: 0053
 Create Date: 2026-05-27
 
-The image cache was wired into the LLM image-search tool (removed in Phase 8).
+The image cache was wired into the LLM image-search tool, which is gone.
 With no producer or consumer left, the table is dropped here.
 """
 from alembic import op