[#493] Fix top 3 performance bottlenecks identified in load testing

[AdaBebe0]

Backlog reference: #493 · perf

Summary

Fix top 3 performance bottlenecks identified in load testing

Context

Caching, indexing, and load-testing work to make sure the platform holds up once real communities are using it concurrently — backed by measured before/after numbers, not guesses.

The path to a public, mainnet launch: KYC/compliance groundwork, price/localization/mobile polish, performance hardening, documentation, and the final production go-live checklist.

Acceptance Criteria

• Fix top 3 performance bottlenecks identified in load testing — implemented as described above.
• A before/after measurement (timing, query plan, load-test result) is included in the PR description.

Definition of Done

• Implemented on a branch and opened as a PR referencing this issue (Closes #493 won't auto-link since this is a repo-internal reference — mention the issue number GitHub assigned instead).
• CI is green (lint, typecheck, tests, build).
• Reviewed against CONTRIBUTING.md conventions (Conventional Commits, code style).
• CHANGELOG.md updated under [Unreleased] if the change is user- or API-visible.
• Merged to main.

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