docs: restructure HTTP API reference

[frydj]

Summary

Restructures Reference > HTTP API from single file to organized directory:

• index.md: API overview and authentication
• ledger-operations.md: Create, list, delete ledgers
• transactions.md: POST /fluree/transact endpoint
• queries.md: POST /fluree/query endpoint (refactored from http-api.md)
• real-time.md: SSE subscriptions
• remote.md: Remote ledger connections

Also updated

• fluree-server-config.md: Expanded configuration reference

Removed

• http-api.md: Content split into directory structure

Test plan

• Verify curl examples work against running server
• Check all endpoint paths are accurate

[frydj]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• docs: add feature showcase examples #71
• docs: add domain example datasets #70
• docs: add feature reference docs #69
• docs: reorganize cookbook #68
• docs: restructure querying reference #67
• docs: restructure HTTP API reference #66 👈 (View in Graphite)
• docs: add advanced topics #65
• docs: add security guides #64
• docs: add modeling guides #63
• docs: add working with data guides #62
• docs: reorganize learn foundations #61
• docs: add getting started guides #60
• docs: add project config & infrastructure #59
• main

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