docs: update README for 0.8

[SamuelSupe]

What changed

• update the project introduction, status, release badge, and non-goals from 0.7 to 0.8
• add a concise 0.8 feature summary covering Kodo compatibility, safe Gateway failover, standard NSQ Stats, durable counters, the 100 MiB boundary, and fail-closed administration
• show the separate standard-producer and Kodo Gateway paths in the architecture overview
• split Kubernetes guidance into standard deployment, Kodo compatibility, and operations sections
• record the v0.8.0 Kodo and three-Broker acceptance results

Why

The repository README already contained detailed Kodo implementation notes, but its headline version and product summary still described RustQueue 0.7. The GitHub landing page did not clearly explain the new 0.8 producer path or its operational boundaries.

Impact

Documentation only. The README now matches the released 0.8.0 code and links directly to the latest release without changing runtime behavior.

Validation

• git diff --check
• verified all relative README links exist
• verified no stale RustQueue 0.7 version text remains
• cross-checked message limits, Gateway count, Stats fields, cleanup behavior, and rollout conditions against current code, Helm values, and acceptance fixtures