Docs reorg - #703

Move all Pipecat tab pages into a unified pipecat/ directory tree:
- get-started/ (introduction, quickstart, build-your-next-bot, ai-tools, next-steps)
- learn/ (12 learning guides)
- fundamentals/ (11 guides + evaluations/)
- features/ (5 feature guides)
- telephony/ (8 telephony guides)
- deployment/ (overview, pattern, platforms/, images/)
- examples/ (overview, recipes)

Update all cross-references across 130+ files and add redirects
for every moved path to preserve existing links.

Promote deployment/pipecat-cloud/ to a top-level pipecat-cloud/
directory and delete the now-empty deployment/ folder. Update all
references in MDX files, OpenAPI JSON specs, and docs.json nav.
Add redirects for all old deployment/pipecat-cloud/ paths.

Move pipecat-cloud/images/ into the shared images/ folder and
convert all relative image paths to absolute /images/... paths.
This makes future page reorganization easier since image references
no longer depend on file location.

…guides

Delete 6 outdated migration guide pages and move API reference and
transport package pages from the API Reference tab into the Pipecat
Clients tab so each SDK group has its intro, reference, and transports
together.

Split the monolithic Flows guide into focused pages (introduction,
quickstart, nodes & messages, functions, actions, context strategies,
state management, examples) under a new Pipecat Flows tab. Move
reference docs from server/frameworks/flows/ to pipecat-flows/reference/
and keep them in the API Reference tab. Add redirects for all old paths.