Add B&W film development chart lookup system

[Copilot]

Implements a lookup table system for B&W film development timing, dilution, and temperature. C41 timing remains unchanged (roll-count based calculation).

Implementation

Database Model

• DevelopmentChart table with unique constraint on (film_stock, developer, iso_rating, dilution_ratio, temperature_celsius)
• Computed property formats seconds → MM:SS display
• Auto-creates table on startup

API Endpoints (/api/dev-chart)

• CRUD operations with filtering/pagination
• POST /lookup - Query by parameters, returns exact match or suggestions
• GET /autocomplete/{films,developers} - Typeahead support
• Race condition protection via IntegrityError catch-and-rollback

Data Seeding

• CSV import script with MM:SS time format support
• Pre-seeded 34 combinations (Ilford HP5+/FP4+/Delta, Kodak Tri-X/T-Max, Fomapan)
• Covers common developers: Ilfosol 3, D-76, HC-110, Rodinal
• Push/pull processing via multiple ISO entries per film

Usage

# Lookup dev time for HP5+ pushed to ISO 800
curl -X POST http://localhost:8200/api/dev-chart/lookup \
  -d '{"film_stock":"Ilford HP5 Plus 400","developer":"Ilfosol 3","iso_rating":800}'
# → {"found": true, "entry": {..., "development_time_formatted": "11:00"}}

# Import CSV data
python migration/scripts/import_dev_chart.py \
  migration/data/dev_chart_seed.csv --db-path backend/data/emulsion.db

Testing

18 integration tests covering CRUD, lookup logic, filtering, pagination, and duplicate prevention.

Original prompt

First read the readme to understand current setup. Then Start a new plan on adding a development-"chart" (but more of a backend/database/lookup tables) for tracking timing, dilution, and temperature required for development. Eventually we will wire its functionality to the front end so it gives the information. Maybe even a chemistry timer widget.

Considerations:
We only plan on supporting two types of chemistry for now: BW and C41. But the timing calculation for C41 is kind of already primitively done using number of existing rolls. And C41 is a standard process where dev time is consistent across all C41 films

So most of our focus would be BW, because permutations of developer and film has different timing and dilution and temperature. For example, for Ilford HP5 films, and if I use Ilfosol 3, it will be 6:30 for iso400, but if I push 1 stop, it'll be 11 minutes. This assumes dilution ratio of 1+4, if it's 1+9, iso 400 will take 8 minutes or something. The point is, there's a lot of input variables to a single output (dev time) and the simplest way I think about is a lookup table.

Then we need to plan out how this can fit into our existing framework. I'd like the ability to quickly add new datapoints from experiment or from reading chemistry data sheets.

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