Detects Dasher v5 data at %APPDATA%\dasher.rc\settings.xml and offers
to import settings on first launch.

V5MigrationService:
- Parses v5 settings.xml (<long>, <bool>, <string> elements)
- Maps 23 bool, 34 long, 9 string parameters to v6 enums
- Transforms DasherFontSize (index → points), start mode (2 bools → enum)
- Defers BP_CONTROL_MODE, SP_INPUT_FILTER, SP_ALPHABET_ID until after
  Realize (matching Dasher-Apple pattern)
- Copies custom alphabet/colour/control/training files (skip-if-exists)
- Marks migration as completed

Startup flow restructured into phases:
1. Create engine (dasher_create)
2. Migration prompt (applies params before Realize)
3. Start engine (dasher_set_screen_size → Realize)
4. Apply deferred parameters
5. Continue UI setup

Updated DasherCore submodule with null guard fix (#19).

Matches Dasher-Apple's macOS implementation pattern from RFC 0005.

Signed-off-by: will wade <willwade@gmail.com>

Privacy tab now has three sections:
1. Analytics (existing) — opt-in toggle, anonymous ID, reset ID
2. Dasher 5 Import — shows detected v5 data status with re-import button
   (re-runs migration and applies params immediately since engine is
   already realized)
3. Reset Settings — red 'Reset to defaults' button that deletes
   dasher_settings.xml so defaults load on next launch

Also fixes crash: all migrated parameters now deferred until after
Realize (LP_NODE_BUDSET etc. trigger handlers that dereference null
m_pDasherModel before Realize)

Signed-off-by: will wade <willwade@gmail.com>

Reset now works immediately without app restart. Destroys the engine,
deletes the saved settings file, recreates the engine with defaults,
re-wires all callbacks, and refreshes the settings panel. Output text
is cleared and UI state (speed, alphabet, control mode) is reloaded.

Signed-off-by: will wade <willwade@gmail.com>