docs: cross-reference manuals from SecurityMode, ZoneType, events, commands

Sprinkle pca-re/docs/manuals/ citations into the four files that map
hardest to user-visible panel behavior, so a reader chasing "why is
this byte 0x03 here" lands on the right manual chapter directly from
the source.

models.SecurityMode
  Per-value comments summarising what each arming mode means at the
  keypad (entry/exit delays, which zones it arms, when to use it).
  Points at the Owner's Manual SECURITY_SYSTEM_OPERATION chapter where
  these semantics are spelled out for end users.

models.ZoneType
  Class docstring now points at the Installation Manual SETUP ZONES
  table where each numeric byte value is named -- the byte values and
  short names we chose match that table one-for-one, so a reader can
  cross-walk the v1 ZoneStatus byte to "PERIMETER" / "AWAY INT" / etc.
  by row.

events.py
  Module docstring adds Cross-references to APPENDIX A (Contact ID
  reporting format) and APPENDIX B (digital communicator code sheet)
  in the Installation Manual -- the central-station codes a panel
  transmits for each AlarmKind correspond directly to those tables.

commands.py
  Module docstring points at the Owner's Manual CONTROL, Scene Commands,
  and SECURITY SYSTEM OPERATION chapters so the reader can tie each
  enuUnitCommand byte to the user-facing keypad path that triggers it.

No code changes; all 387 tests still pass.

src/omni_pca/commands.py

@@ -39,6 +39,19 @@ The reply (ExecuteSecurityCommandResponse, opcode 75) carries a single
 status byte at ``payload[0]`` whose values are listed in
 ``enuSecurityCommnadResponse.cs`` — :class:`SecurityCommandResponse`
 mirrors that enum.
+
+Cross-references (HAI OmniPro II Owner's Manual):
+    Chapter "CONTROL" (pca-re/docs/owner_manual/05_CONTROL/) documents
+        the user-facing keypad keys that map to these commands —
+        e.g. UNIT_ON/OFF + UNIT_LEVEL are what a homeowner triggers via
+        the "Control → 1 (Unit)" menu, SHOW_MESSAGE_WITH_BEEP is
+        invoked from "Control → Message → Show".
+    Chapter "Scene Commands" (06_Scene_Commands/) covers
+        COMPOSE_SCENE and the per-room scene-recall path.
+    Chapter "SECURITY SYSTEM OPERATION" (03_SECURITY_SYSTEM_OPERATION/)
+        documents what each SecurityMode byte (0-6) means at the user
+        level — the arming menu, entry/exit-delay semantics, and which
+        zones each mode arms.
 """
 
 from __future__ import annotations

src/omni_pca/events.py

@@ -29,6 +29,16 @@ References (decompiled C# source):
                                        — bit-mask classifier we mirror below
     clsText.cs:1693-1911 (GetEventText)
                                        — per-category sub-field extraction
+
+Cross-references (HAI OmniPro II Installation Manual):
+    APPENDIX A — CONTACT ID REPORTING FORMAT (p68): the Contact ID
+        event codes the panel transmits to a central monitoring station
+        for each :class:`AlarmKind`. The class names below mirror those
+        codes one-for-one. (pca-re/docs/manuals/installation_manual/
+        10_APPENDIX_A_CONTACT_ID_REPORTING_FORMAT/)
+    APPENDIX B — DIGITAL COMMUNICATOR CODE SHEET (p69-73): the 4/2 and
+        3/1 reporting-format code tables. Useful when correlating a
+        SystemEvents word with what a central station would see. (12_…)
 """
 
 from __future__ import annotations

src/omni_pca/models.py

@@ -490,18 +490,25 @@ class ObjectType(IntEnum):
 class SecurityMode(IntEnum):
     """Area security mode (enuSecurityMode.cs).
 
-    Values 9..14 are the "arming in progress" variants the panel reports
-    while a delayed-arm timer is running.
+    The first 7 values are what the user actually picks at the keypad
+    when arming. Values 9..14 are the "arming in progress" variants the
+    panel reports while a delayed-arm timer is running.
+
+    Reference: HAI OmniPro II Owner's Manual, *Security System
+    Operation* chapter (pca-re/docs/owner_manual/
+    03_SECURITY_SYSTEM_OPERATION/) — the user-facing semantics of each
+    mode (entry/exit delays, which zones are armed, when to use which)
+    come from there.
     """
 
-    OFF = 0
-    DAY = 1
-    NIGHT = 2
-    AWAY = 3
-    VACATION = 4
-    DAY_INSTANT = 5
-    NIGHT_DELAYED = 6
-    ANY_CHANGE = 7
+    OFF = 0            # disarmed; resets fire / emergency alarms, silences sirens
+    DAY = 1            # perimeter armed, interior motion NOT armed, entry delay
+    NIGHT = 2          # perimeter + non-sleeping-area motion armed, NO entry delay
+    AWAY = 3           # everything armed, both exit + entry delays
+    VACATION = 4       # same as AWAY but for multi-day absences
+    DAY_INSTANT = 5    # DAY with no entry delay (instant alarm on perimeter)
+    NIGHT_DELAYED = 6  # NIGHT with entry delay on entry-exit zones
+    ANY_CHANGE = 7     # programming-condition wildcard, NOT a real arming state
     ARMING_DAY = 9
     ARMING_NIGHT = 10
     ARMING_AWAY = 11
@@ -560,6 +567,13 @@ class ZoneType(IntEnum):
     the temperature/humidity sensors and a handful of utility types. Any
     raw byte value still round-trips through ``ZoneStatus.zone_type`` —
     it just won't have a named enum member.
+
+    Reference: HAI OmniPro II Installation Manual, *Installer Setup →
+    SETUP ZONES → ZONE TYPES* table (pca-re/docs/manuals/
+    installation_manual/04_INSTALLER_SETUP/INSTALLER_SETUP.md, p38-39).
+    The byte values and short names here match the installer-setup
+    keypad selections one-for-one (e.g. ``PERIMETER = 1`` is the same
+    "PERIMETER" the installer scrolls to when setting Z1..Z176 types).
     """
 
     ENTRY_EXIT = 0