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/0049_conversation_curator_summary.py

@@ -4,7 +4,7 @@ Revision ID: 0049
 Revises: 0048
 Create Date: 2026-05-22
 
-Phase 3 of the conversation+curator architecture (Fable #172). The
+Part of the conversation+curator architecture. The
 curator's final summary line (≤ 240 chars) is persisted here so the
 NEXT chat turn can include it in the system prompt. This is the
 feedback loop that closes the architecture — without it, the chat