Reservation lease time; reservations by MAC address or client ID

- A reservation can have its own lease time (--lease-time, the
  reservation dialog), over the subnet's. Schema migration 6.
- A reservation with a MAC address and a client ID matches either one
  (a dual-boot machine sends two client IDs from one MAC); before, it
  was found by MAC and then refused. A lease of the reserved address by
  the client's other identity counts as its own.
- The Leases page shows a client's client ID; reserving a lease uses
  both, or one with --by / the dialog's choice.

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

docs/api.md

@@ -111,7 +111,7 @@ out. `lease_time` 0 means the settings'.
 | | |
 |---|---|
 | `GET /reservations[?subnet=REF]` | each with `subnet_id`, `subnet` and its current `lease` |
-| `POST /reservations` | `{"ip", "mac", "client_id", "hostname", "options", "disabled", "comment"}`; `ip` and `mac` or `client_id` needed |
+| `POST /reservations` | `{"ip", "mac", "client_id", "hostname", "options", "lease_time", "disabled", "comment"}`; `ip` and `mac` or `client_id` needed (with both, either matches); `lease_time` 0 is the subnet's |
 | `GET`, `PATCH`, `DELETE /reservations/{ref}` | by ID, address, or MAC address (when it has one reservation) |
 
 ### Leases and activity
@@ -121,7 +121,7 @@ out. `lease_time` 0 means the settings'.
 | `GET /leases[?subnet=&state=&interface=&q=]` | every lease, with its state now (`active`, `expired`, `released`, `declined`), `subnet` and its reservation, and `last_seen` when the client last answered a ping (left out if it never has); `q` searches address, MAC and host name |
 | `GET /leases/{ip}` | one |
 | `DELETE /leases/{ip}` | forget it (audited) |
-| `POST /leases/{ip}/reserve` | make it a reservation; optional `{"hostname", "comment"}` |
+| `POST /leases/{ip}/reserve` | make it a reservation; optional `{"hostname", "comment", "by"}`, `by` being `mac`, `client_id` or `both` (the default) |
 | `GET /events[?mac=&subnet=&interface=&limit=]` | the latest DHCP messages, newest first (the last 1000 are kept in memory). `subnet` (ID, name or prefix) keeps messages for its addresses, and those without an address on its interface |
 
 ### History and import