WJ-1139: add forum schema, prune references, and seed sequences

[Syxless]

Implements the forum schema (groups, categories, threads, locks, posts, post revisions) with site-level composite FKs, actor fields, soft-deletes, discussion-thread uniqueness, and indexes for ordering/activity/lookups.
Adds forum compatibility ID bumps in the seeder.
Updates TextService::prune() to keep forum post revision text hashes.

Tests: ran.

[emmiegit]

Ah I see, temporary measure until new src/models files are generated. I'll do that in a separate PR because the autogen tool needs some manual correction unfortunately.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 15 lines in your changes missing coverage. Please review.
✅ Project coverage is 2.27%. Comparing base (be83e2d) to head (c731882).
⚠️ Report is 18 commits behind head on develop.

Files with missing lines	Patch %	Lines
deepwell/src/database/seeder/mod.rs	0.00%	9 Missing ⚠️
deepwell/src/services/text.rs	0.00%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           develop   #2613      +/-   ##
==========================================
- Coverage     2.27%   2.27%   -0.01%     
==========================================
  Files          164     164              
  Lines        10227   10242      +15     
==========================================
  Hits           233     233              
- Misses        9994   10009      +15     

Files with missing lines	Coverage Δ
deepwell/src/services/text.rs	0.00% <0.00%> (ø)
deepwell/src/database/seeder/mod.rs	0.00% <0.00%> (ø)

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