fix(wake): #925 framework-ship canon fallback-wake (systemd timer + schema bound + A10 install/validate) — F7 out of the box (#931)

Co-authored-by: jason.woltje <jason@diversecanvas.com>
Co-committed-by: jason.woltje <jason@diversecanvas.com>

packages/mosaic/framework/defaults/wake-watch-list.schema.json

@@ -103,6 +103,10 @@
             "type": "string",
             "description": "Operator-supplied duration (e.g. '5m', '30m', '4h'). Symbolic tier is set by the operator, not the framework."
           },
+          "fallback_cadence": {
+            "type": "string",
+            "description": "OPTIONAL, additive (schema_version 1, backward-compatible — omitting it is valid). The per-class cadence bound for the framework-shipped canon FALLBACK WAKE (F7 replacement-before-retirement, EPIC #892): the low-frequency SAFETY-wake timer (mosaic-wake-fallback.timer) that fires the canon drain INDEPENDENT of the event-driven detector, so a stalled detector cannot silently starve delivery. The A10 installer reads this per-class value and writes it as the fallback timer's OnUnitActiveSec via the blank-reset drop-in (exactly one effective OnUnitActiveUSec). SYMBOLIC — an operator-supplied duration (e.g. '30m', '1h', '4h'); the framework bakes in no numeric. Config, not code. Should be no tighter than this tier's `fallback_bound` (the safety wake is a floor, never the primary mechanism)."
+          },
           "quiet_hours_may_suppress": {
             "type": "boolean",
             "default": false,