feat(plan): register the plan session-projection unit

plan-mode contributes the RFC's complete double-event example: command/run
records named plan set the wanted target (off -> false, else true),
plan/mode commits and clears it, and view derives {active, pending}.
Pending is thereby a pure replay quantity recovered from the log alone.
The plan key merges into SessionProjectionMap from src/types.ts, served
through the new ./types and ./client outlets (session-title template);
compositions without the registry are unaffected.

packages/plan/plan-mode/tsconfig.json

@@ -32,6 +32,9 @@
     {
       "path": "../../ui/commands"
     },
+    {
+      "path": "../../session-projection/session-projection"
+    },
     {
       "path": "../../support/invariants"
     }