chore: remove unused CI FEATURES build-arg and dedupe compose image build

[crazywriter1]

Summary

• Drop the unused FEATURES build-arg from PR and release Docker workflows. The Dockerfile does not declare ARG FEATURES, and cargo build does not pass --features, so the matrix values had no effect (leftover from an older client layout).
• Build the node image once in Compose: execution builds base-node:local, and node reuses the same image instead of running a second identical build.

Motivation

CI suggested feature flags were being applied when they were not. Locally, docker compose up --build compiled the same Dockerfile twice for execution and node, doubling build time without changing runtime behavior.

Changes

• .github/workflows/pr.yml — remove features matrix field and build-args: FEATURES=...
• .github/workflows/docker.yml — same
• docker-compose.yml — add image: base-node:local to both services; keep build only on execution

Test plan

• Compose structure verified (single build on execution, shared base-node:local image)
• CI workflows no longer pass unused FEATURES build-arg
• docker compose config / docker compose build — skipped locally (Docker not installed in WSL)
• PR CI Docker build (amd64 + arm64) — pending after PR open

[cb-heimdall]

🟡 Heimdall Review Status

Requirement	Status	More Info
Reviews	🟡 0/1	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 0 Sum 1