docs: document v3 release and v6 plugins

[rustatian]

• Add v3 release notes and a focused v2025-to-v3 upgrade guide. Keep configuration and behavior details in the reference pages.

• Update HTTP and gRPC coverage for middleware order, PROXY protocol, rate limiting, compression, static caches, and reflection.

• Document named Jobs pools, NSQ, named AMQP connections, Redis locks, and queue/storage behavior.

• Update logging, metrics, tracing, health checks, Service, Centrifuge, and Temporal guidance.

• Document the API repository split, v6 Go contracts, and the RoadRunner /v3 module.

• Use v3 download URLs, image tags, imports, and command output throughout the current guides.

• Cover the default Zstd and Protoreg bundle additions in chore: release-v3 roadrunner#2410.

• Describe the shared Jobs queue: the wait for a free slot, arrival order for equal priorities, the 100000 default pipeline_size and the poller count for a pool without num_workers ([🐛 BUG]: jobs: priority_queue.Insert() busy-loops a full CPU core while the pipeline is over pipeline_size (any sustained backlog) roadrunner#2411).

• State that RoadRunner v3 does not support the TCP plugin. Applications that use it stay on RoadRunner v2025, and the tcp:// transport for RPC and worker relays is unchanged.

[Copilot]

🟡 Changes recommended

There are a couple of documentation consistency/clarity issues (HTTP zstd page title format and static cache behavior description) that should be corrected to avoid confusing readers.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

This PR consolidates and expands RoadRunner v3-related documentation by adding new docs pages/features (HTTP zstd middleware and gRPC interceptors) and updating existing pages to reflect newer configuration formats and behaviors.

Changes:

• Added new documentation pages for HTTP zstd middleware and gRPC unary interceptors, and linked them from navigation and existing guides.
• Reworked AMQP jobs pipeline documentation to describe versioned pipeline config formats (v2 nested exchange/queue vs legacy flat) and added operational notes (read-only RabbitMQ, RPC declaration behavior).
• Updated HTTP docs to include zstd in the HTTP middleware reference and refreshed static middleware caching/ETag documentation.

File summaries

File	Description
SUMMARY.md	Adds nav entries for HTTP zstd and gRPC Interceptors.
queues/amqp.md	Updates AMQP pipeline config docs (v2 nested format, legacy keys, permissions/RPC notes, migration/next links).
http/zstd.md	New page documenting HTTP zstd middleware availability, config, and behavior.
http/static.md	Updates static middleware docs with cache/prefix options and corrected ETag behavior description.
http/http.md	Adds zstd to the allowed HTTP middleware list and notes build requirement.
grpc/interceptors.md	New page documenting interceptor contract, config, ordering, and build examples.
grpc/grpc.md	Adds a cross-link to the new interceptors documentation.

Review details

• Files reviewed: 7/7 changed files
• Comments generated: 2
• Review effort level: Lite

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