docs(channel-deployment): rebrand COCO → OpenMax in EN & ZH guides

[Eriche985]

Summary

Per the brand upgrade to OpenMax, replace all remaining COCO brand mentions in both language versions of the channel-deployment guide (docs/getting-started/channel-deployment.md + docs/zh/getting-started/channel-deployment.md).

Changed (brand copy only)

• COCO Dashboard → OpenMax Dashboard (headings, steps, tables, image alt text) — matches the convention already used in the MS Teams section
• COCO Account / COCO账号 → OpenMax Account / OpenMax账号
• Example names: COCO AI Employee / COCO AI 员工 / My COCO AI / COCO AI → OpenMax equivalents; my_coco_ai_bot → my_openmax_ai_bot; bot handle coco-ai-employee → openmax-ai-employee; COCO Bot Secret → OpenMax Bot Secret
• MS Teams manifest sample (ZH): developer name COCO → OpenMax, app name & description
• Prose: "your COCO agent" → "your OpenMax agent", "COCO handles everything" / "由 COCO 代为处理" → OpenMax

Deliberately NOT changed

• Live URLs/domains: icoco.ai/dashboard, docs.icoco.ai/*, <subdomain>.icoco.ai webhook examples (product URLs still live on these domains)
• Image file paths (e.g. /coco-dashboard-*.png) — renaming images would re-trigger the CDN cache issue fixed in fix(channel-deployment): cache-bust MS Teams tutorial images (rename to -v2) #178; filenames are invisible to readers
• GitHub release asset links (github.com/openmaxai/coco-materials/...)

Verification

• grep -i coco residue check: zero brand-text matches left; remaining matches are only domains/file paths/repo URLs
• vitepress build passes locally (EN + ZH render clean)

109 replacements per side, text-only, no structural/link/anchor changes.

🤖 Generated with Claude Code

[tyler-0xffff]

Review: PASS ✅

Verified against 3 checkpoints:

① Brand text only, no collateral damage

• Image withBase(...) count identical to main: EN 85/85, ZH 67/67
• HTTP link count identical to main: EN 30/30, ZH 27/27
• All product URLs preserved (icoco.ai/dashboard, docs.icoco.ai/privacy-policy, docs.icoco.ai/user-agreement, webhook subdomains), image file paths untouched (correctly avoids re-triggering the #178 CDN-cache-404 issue), GitHub release asset links untouched.

② Full zh + en coverage, no brand-text residual

• Residual grep on both files: no remaining brand-text COCO. All leftover "coco" strings are exclusively the intentionally-kept icoco.ai domain, coco-materials release assets, and /coco-dashboard-*.png image paths.
• Consistent with existing MS-Teams section wording (COCO Dashboard → OpenMax Dashboard, example names, Teams manifest name/developer/description, Azure bot handle, secrets label).

③ Build

• vitepress build docs → exit 0, pages rendered, sitemap generated. (Pre-existing cosmetic @import order warning in theme CSS, unrelated to this PR.)

Post-deploy I'll verify live on both docs.icoco.ai and docs.openmax.com.