Add configurable manual feed amount and move global feed settings out of schedules

[bschlagheck]

Problem

Manual feeding is currently fixed to 1 portion unit.

This affects both:

• the Feed Now action in the web UI
• the hardware button manual feed action

At the same time, the global portion_unit_grams setting is currently placed inside the schedules section, even though it also affects manual feeding and button-triggered feeding.

Goal

• Allow configuring the manual feed amount in the UI
• Persist that value in device config
• Use the same saved manual feed amount for both:
  • Feed Now
  • hardware button manual feeding
• Move global feed settings out of the schedules section
• Increase portion sliders from 1..5 to 1..10 consistently across the system

Proposal

Add a new global feed settings block above the schedules section.

The block should contain:

• Portion size (g per unit)
• Manual feed amount

The portion_unit_grams setting should no longer live inside the schedules section.

Manual feeding should use a saved manual_portion_units config value instead of being hardcoded to 1.

Technical outline

1. Config

   • Add persistent manual_portion_units
   • Default to 1

2. Firmware

   • POST /feed should use stored manual_portion_units
   • hardware button manual feed should use stored manual_portion_units
   • extend validation for portion units from 1..5 to 1..10

3. Web API

   • include manual_portion_units in GET /config
   • accept and validate manual_portion_units in POST /config

4. Frontend

   • add a new Feed settings block above schedules
   • move Portion size (g per unit) into that block
   • add UI control for Manual feed amount
   • update displayed gram calculations accordingly

5. Import / Export

   • include manual_portion_units in config export/import

6. Mock

   • extend mock config and validation
   • use stored manual amount in mock manual feed behavior

Acceptance criteria

• The manual feed amount can be configured in the UI
• The value is saved persistently on the device
• Feed Now uses the saved manual feed amount
• hardware button manual feeding uses the same saved manual feed amount
• Portion size (g per unit) is no longer shown inside the schedules section
• Portion sliders support 1..10 for schedules and manual feeding
• Import/export includes the new manual feed config
• Mock behavior matches the real API behavior