Codify plan-save ordering and add plan execution summaries

The plan for this build was written to docs/plans/ only after Step 0's
implementation had already started, instead of as its own first action
right after ExitPlanMode. CLAUDE.md said *where* to save plans but not
*when* relative to other work, so that ordering wasn't actually enforced.
Makes it explicit: copying the plan into docs/plans/ and committing it is
its own checkpoint that blocks starting Step 0.

Also adds a docs/plans-executions/ convention: one running, chronological
summary file per plan, appended to after each completed step, for a
human-readable narrative of how the plan actually went (judgment calls,
spec gaps, surprises) without duplicating the plan or the diff.

Backfills the Step 0 entry for the proxy-operator plan retroactively.

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

.claude/settings.json

@@ -39,11 +39,13 @@
       "Bash(mkdir -p docs/plans && date \"+%Y-%m-%d-%H%M\")",
       "Bash(go install *)",
       "Bash(go env *)",
-      "Bash(git rm *)"
+      "Bash(git rm *)",
+      "Bash(mkdir -p /Users/jan.novak/srv/go/egress-proxies-operator/docs/plans-executions)"
     ],
     "additionalDirectories": [
       "/Users/jan.novak/srv/go/egress-proxies-operator/.claude",
-      "/Users/jan.novak/srv/go/egress-proxies-operator/docs/plans"
+      "/Users/jan.novak/srv/go/egress-proxies-operator/docs/plans",
+      "/Users/jan.novak/srv/go/egress-proxies-operator/docs"
     ]
   }
 }