Migrate Hackster to Pydantic v2

[dimoschi]

Types of changes

What types of changes does your code introduce?
Put an x in the boxes that apply.

• Bugfix (non-breaking change which fixes an issue).
• New feature (non-breaking change which adds functionality).
• Breaking change (fix or feature that would cause existing functionality not to work as expected).
• Documentation Update (if none of the other choices applies).

Proposed changes

• migrate the project from Pydantic v1 to Pydantic v2 and move settings loading to pydantic-settings
• harden the settings layer by using a strict nested env contract for BOT, DATABASE, CHANNEL, and ROLE
• replace assert-style config validation with explicit validation errors
• remove Pydantic usage from src/core/constants.py
• update test fixtures and config tests for the nested env naming scheme

This PR also keeps the settings surface compatible with the current code shape by preserving settings.bot, settings.database, settings.channels, settings.roles, and settings.role_groups.

Operational note: this changes the new config contract to nested env keys such as BOT__TOKEN, DATABASE__HOST, CHANNEL__SR_MOD, and ROLE__VERIFIED. During rollout, the old flat env keys can coexist in Vault alongside the new nested ones so the current production bot and this branch can run safely in parallel.

Checklist

Put an x in the boxes that apply.

• I have read and followed the CONTRIBUTING.md
  doc.
• Lint and unit tests pass locally with my changes.
• I have added the necessary documentation (if appropriate).

Additional context

Full test suite result on this branch:

• PYTHONPATH=. uv run pytest
• 276 passed, 12 warnings

The warnings are pre-existing test/runtime warnings and were not introduced by this migration.

[codecov]

Codecov Report

❌ Patch coverage is 97.29730% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 65.18%. Comparing base (628170a) to head (fd63086).

Files with missing lines	Patch %	Lines
src/core/config.py	96.33%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #184      +/-   ##
==========================================
+ Coverage   65.15%   65.18%   +0.02%     
==========================================
  Files          52       52              
  Lines        3042     3056      +14     
==========================================
+ Hits         1982     1992      +10     
- Misses       1060     1064       +4     

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[0xRy4n]

Sorry this took so long to look at.

Changes look fine to me, only thing worth noting is that .docker.env did not get it's variables updated to match the changes to .test.env -- It still uses the MYSQL_ prefix instead of the DATABASE__ prefix.

I've added that small change and also resolved the conflicts with main.