docs(m66): nanos shape + posture-dispatched stage rates + SUPPORT_EMAIL snippet

[indykish]

Summary

Companion docs PR for usezombie/usezombie#314. The lead PR retires the BYOK term, switches the canonical billing unit from cents to nanos (1/1,000,000,000 USD), introduces a posture-dispatched stage rate gradient, and pins a single canonical SUPPORT_EMAIL. This PR moves the docs site in lockstep.

• snippets/rates.mdx — display exports rewritten to mirror the new four-constant Zig/TS/JS shape identifier-for-identifier: STARTER_CREDIT ($5, unchanged), EVENT_RATE ("free", was $0.01), STAGE_PLATFORM ($0.001), STAGE_SELF_MANAGED ($0.0001). Cross-tier parity rule is load-bearing — a future rate bump fails pin tests in Zig + TS + JS until this snippet is updated.
• snippets/contact.mdx — new file exporting SUPPORT_EMAIL = "usezombie@agentmail.to". Fifth replica of the per-runtime constant added in the lead PR (Zig backend, website TS, app TS, CLI JS, and now docs MDX). Future address rotations land as a coordinated five-place bump.
• changelog.mdx — new <Update label="May 11, 2026"> block at the top documenting the nanos rebill, the posture-dispatched stage gradient ($0.001 platform → $0.0001 self-managed = 10× cheaper to scale), the BYOK term retirement, the column/constant renames, and upgrade notes (balance_cents → balance_nanos, mode: "byok" → mode: "self_managed", make down && make up for local dev).

Historical-entry carve-out

The May 9, 2026 (M65) entry described "one number per surface" under the pre-M66 rate table. Without intervention, the rates.mdx rewrite would have silently rewritten that historical entry's meaning. The fix: define EVENT_RATE_M65 + STAGE_RATE_M65 placeholders once at the import header, used inline in the affected entry only. Lightweight; the placeholders live above the shared imports so the pattern is easy to spot in future archive passes.

Broken cross-reference fix

The M63_003-era entry referenced billing_and_byok.md — the lead PR renames that file to billing_and_provider_keys.md. Updated the link target to billing_and_provider_keys.md (then named billing_and_byok.md) so the reader can follow the link without losing the historical context.

Test plan

• Mintlify <Update> voice — Bold lead-noun bullets, no marketing words, code-name backticks, error codes / endpoint paths / column names preserved
• Rate constants flow through the three pinned files: src/state/tenant_billing.zig, ui/packages/website/src/lib/rates.ts, ~/Projects/docs/snippets/rates.mdx (all paired in the lead PR + this PR)
• Historical M65 entry continues to render with the old $0.01 / $0.10 rates via _M65 placeholders
• Cross-reference billing_and_byok.md → billing_and_provider_keys.md link target updated with parenthetical historical context

🤖 Generated with Claude Code

Greptile Summary

This PR updates the docs site to mirror the M66 backend changes: billing unit switched from cents to nanos, stage rates split into a posture-dispatched two-rate gradient, BYOK terminology retired, and a new canonical SUPPORT_EMAIL snippet introduced.

• snippets/rates.mdx — four-constant rewrite: EVENT_RATE → \"free\", STAGE_RATE replaced by STAGE_PLATFORM ($0.001) and STAGE_SELF_MANAGED ($0.0001); identifier-for-identifier parity with the Zig/TS/JS lead PR.
• snippets/contact.mdx — new file exporting SUPPORT_EMAIL; the constant is defined and documented but not yet imported by any existing docs page, so the two pre-existing hardcoded email literals (changelog.mdx <Tip> and index.mdx) remain outside the canonical constant.
• changelog.mdx — M66 breaking-change entry added; historical M65 pricing preserved via inline _M65 placeholder constants; billing_and_byok.md cross-reference updated with parenthetical historical context.

Confidence Score: 5/5

Safe to merge — all three files are documentation-only changes with no runtime impact.

The rate-constant rewrite in snippets/rates.mdx is straightforward and consistent with the lead PR's four-constant shape. The M66 changelog entry is well-structured with correct historical placeholder usage for the M65 entry. The only gap is that snippets/contact.mdx is never imported by any existing page, leaving pre-existing hardcoded email literals disconnected from the new canonical constant — but this is a deferred wiring issue, not a content error.

snippets/contact.mdx — the canonical SUPPORT_EMAIL constant is not yet connected to the two pre-existing hardcoded email literals in changelog.mdx and index.mdx.

Important Files Changed

Filename	Overview
snippets/rates.mdx	Rewrites display constants to match the four-constant nanos+gradient shape: EVENT_RATE now "free", STAGE_RATE split into STAGE_PLATFORM and STAGE_SELF_MANAGED. Clean and consistent with the cross-tier parity rule.
snippets/contact.mdx	New file exporting SUPPORT_EMAIL. Correct definition and well-commented, but no existing docs page currently imports this constant, leaving pre-existing hardcoded email literals in changelog.mdx and index.mdx disconnected from the canonical snippet.
changelog.mdx	Adds the M66 breaking-change entry with correct rate constant imports, inline historical M65 placeholders, and the billing_and_byok.md → billing_and_provider_keys.md cross-reference fix. All M65 occurrences of EVENT_RATE and STAGE_RATE correctly redirected to _M65 placeholders.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A["Lead repo rate constants\n(tenant_billing.zig / rates.ts / types.ts / billing.js)"]
    B["snippets/rates.mdx\nSTARTER_CREDIT, EVENT_RATE,\nSTAGE_PLATFORM, STAGE_SELF_MANAGED"]
    C["changelog.mdx\nimport from rates.mdx"]
    D["Other docs pages\nimport from rates.mdx"]
    E["snippets/contact.mdx\nSUPPORT_EMAIL"]
    F["changelog.mdx Tip — hardcoded"]
    G["index.mdx — hardcoded"]
    H["Future docs pages\nimport from contact.mdx"]

    A -->|"cross-tier parity rule\npaired PR"| B
    B --> C
    B --> D
    E -.->|"no importer yet"| H
    E -. "bypassed" .-> F
    E -. "bypassed" .-> G

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Prompt To Fix All With AI

Fix the following 1 code review issue. Work through them one at a time, proposing concise fixes.

---

### Issue 1 of 1
snippets/contact.mdx:10
**`SUPPORT_EMAIL` defined but never imported**

`snippets/contact.mdx` exports `SUPPORT_EMAIL`, but a repo-wide search shows no docs page imports it. Two hardcoded `usezombie@agentmail.to` literals remain live — one in `changelog.mdx` line 18 (`<Tip>` block) and one in `index.mdx` line 9. A future email rotation updates the snippet but leaves those hardcoded links stale, which defeats the stated purpose of the coordinated five-place bump.

_{Reviews (2): Last reviewed commit: "docs(changelog): drop internal rule iden..." | Re-trigger Greptile}

[indykish]

Lead PR: usezombie/usezombie#314