chore!: improve data fetching & proposal form

[helmturner]

Pull Request Template

• Fixes: #240
• Fixes: #238
• Closes: #242
• Closes: #228

This also gets us part of the way toward #239 by creating a pattern for handling fetch errors. Abstracting the patterns in NewProposalFormError would be the next step to closing it.

Description

• unify/simplify fetching with react-hook-forms + zod validation
• autogenerate client SDK/validators w/ openapi-zod-client & zodios
• automatically populate user data from session
• fix(api-spec): make Authorization token header type string
• fix(api-spec): add success property to POST /proposals response schema
• fix(api-spec): clarify proposal types
• consolidate "Topic", "Project", & "InitiativeData" API models as "Proposal"

Screenshots (if appropriate):

Please review and suggest any further insights, improvements, or modifications needed.