Close alpha readiness checklist and define beta entry criteria

[adolago]

Problem

Project readiness artifacts still indicate alpha and unresolved launch items.

Why this blocks beta

Release communication and readiness gates are inconsistent with beta expectations.

Evidence

• README.md:14
• docs/ALPHA_LAUNCH_CHECKLIST.md:5
• docs/ALPHA_READINESS_ISSUES.md:10

Acceptance criteria

• Resolve or explicitly defer all alpha readiness blockers with owner + target milestone.
• Update readiness checklist status with objective pass/fail criteria.
• Update README positioning and release notes once beta gating conditions are met.
• Document beta entry criteria and sign-off process in a single canonical doc.

Dependencies

• Distributed controller marks work units completed without executing tasks #787
• Cluster manager startup/state are stubbed (leader/load telemetry missing) #788
• Agent runtime/client RPC paths are stubbed (AgentNotRunning TODOs) #789
• Expand CI matrix to gate major optional feature bundles #791
• Automate currently manual high-risk test suites before beta #792