fix(devex): make just up resilient across local worktrees

[HendrikReh]

Summary

• Switched Docker entrypoints in Justfile to a shared Compose project (${APEX_COMPOSE_PROJECT_NAME:-apex}) so just up/down reuse one local stack across worktrees instead of racing for the same host ports.
• Updated the destructive readiness degradation test to target the explicit shared Compose project and repo-level compose file when stopping/starting Qdrant.
• Documented the shared-stack workflow in the testing guide and surfaced APEX_COMPOSE_PROJECT_NAME in .env.example.

Related Issue

• Beads: apex-73n

Scope

Changed files

• Justfile - make Docker/test entrypoints use a shared Compose project and propagate the project name into test commands
• crates/rag-server/tests/health_degraded.rs - target explicit Compose project/file for Qdrant stop/start
• docs/howto/testing.md - document shared local stack workflow and troubleshooting command
• .env.example - add APEX_COMPOSE_PROJECT_NAME default

Out of scope

• No changes to application runtime behavior, routing logic, retrieval, or API contracts
• No migration or persistence-layer changes

Validation

Check	Command	Result
Targeted degraded-readiness behavior	APEX_COMPOSE_PROJECT_NAME=apex CARGO_TARGET_DIR=target/itest cargo test -p rag-server --test health_degraded -- --ignored --nocapture --test-threads=1	pass (1 passed)
Offline routed benchmark path	just agentic-eval	pass (1 passed)
Compilation	CARGO_TARGET_DIR=target/check cargo check -p rag-server	pass
Format/lint/full suite	just test	not run -- user decision/policy
Full integration matrix	just integration-test	not run -- targeted verification only

Risk and Rollback

• Risk: medium -- changes central developer entrypoints (Justfile) and destructive test Docker targeting, but are constrained to local verification workflow.
• Rollback: revert Justfile, crates/rag-server/tests/health_degraded.rs, docs/howto/testing.md, and .env.example to previous commit state.

Reviewer Focus

1. Confirm shared Compose project handling is correct for multi-worktree workflows and still respects APEX_COMPOSE_PROJECT_NAME overrides.
2. Confirm health_degraded test stop/start commands now consistently target the same stack that just up starts.

Generated with Codex

[HendrikReh]

@codex review this PR

[HendrikReh]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. 🎉

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[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Another round soon, please!

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