feat(readiness): Maturity "report card" output with tiered levels and next-step guidance

Problem

The current readiness report outputs pass/fail criteria grouped by pillar (repo health, AI tooling). This is useful for engineers, but not actionable enough for customer-facing engagements. Field teams (FDEs, CSAs) need a higher-level view that maps a repo's current state to a named maturity tier with clear guidance on what to do next.

In the AgentRC futures discussion with Barton Mathis, he described a ring-based maturity model for AI adoption. AgentRC's readiness scoring already captures the underlying signals — what's missing is a presentation layer that synthesizes those signals into a maturity narrative.

Proposal

1. Define maturity tiers

Map readiness scores to named tiers (names TBD, example below):

Thresholds should be configurable via policy or config.

2. Add "next steps" to report output

For each tier below Advanced, surface the top 3 actions that would move the repo to the next tier — derived from the highest-impact failing criteria (using existing impact and effort metadata).

Example output:

Maturity: Structured (score: 52/100)

To reach Optimized:
  1. Add custom instructions (.github/copilot-instructions.md) — high impact, low effort
  2. Configure MCP servers for your toolchain — high impact, medium effort
  3. Add a lockfile for dependency pinning — medium impact, low effort

3. Surfaces

• CLI: agentrc readiness --report-card (or integrate into default output)
• CLI HTML report: Add a hero banner with tier name + score + next steps
• Webapp: Replace or augment the current score display with tier visualization
• JSON output: Include maturity.tier, maturity.score, maturity.nextSteps[] in the machine-readable output

Context

• Discussed in "AgentRC: Quick Chat on Futures" meeting
• Related: existing readiness pillar system in packages/core/src/services/readiness/

Start by reading the existing readiness pillar system in packages/core/src/services/readiness/ and trace how readiness scores reach the CLI, HTML report, webapp, and JSON output. Define the maturity tiers, configurable thresholds, and next-step selection across those surfaces. Done means the report card is represented consistently in each requested output, including tier, score, and next steps.