Define agent harness browser receipt surface

[mdheller]

Summary

Adds the BearBrowser receipt surface and first machine-checkable browser receipt fixture set for the agent harness operating model.

This aligns browser automation with SourceOS execution receipts, AgentPlane evidence packs, Policy Fabric gates, Memory Mesh artifact pointers, SCOPE-D checks, and Delivery Excellence scoreboards.

Scope

• Adds docs/agent-harness-browser-receipts.md.
• Adds schemas/agent-harness-browser-receipts.schema.json.
• Adds examples/agent-harness-browser-receipts.example.json.
• Adds scripts/bearbrowser-verify-agent-harness-receipts.py.
• Adds focused CI workflow .github/workflows/agent-harness-browser-receipts.yml.
• Defines BrowserSessionReceipt, BrowserActionReceipt, BrowserDownloadReceipt, and BrowserCredentialUseReceipt semantics.
• Defines policy requirements for login, credential use, form submit, downloads/uploads, account changes, message sends, purchase/order/ticket creation, and headless/hidden modes.
• Defines Delivery Excellence projections and SCOPE-D browser-risk checks.

Validation

• Branch diff is 5 commits ahead, 48 behind current main; update/rebase before merge.
• Changed files are limited to docs, schema, example, verifier, and focused workflow.
• No runtime behavior changed.

Related

• Define agent harness execution receipt boundary sourceos-spec#93
• Add agent harness delivery operating model SocioProphet/delivery-excellence#9
• Add agent harness metric contracts SocioProphet/delivery-excellence-automation#7
• Define agent harness runtime contract map SocioProphet/agentplane#107
• Define agent harness policy gate model SocioProphet/policy-fabric#60
• Define agent harness memory ledger contract SocioProphet/memory-mesh#23