chore(docs): document how to install deno and related certs for agents (commontoolsinc#2030)

* Add minimal test reproducing ConflictError warnings

- Identified that ~42 ConflictError warnings appear during parallel test execution
- Root cause: pattern-harness.ts uses shared DID for all tests
- Conflicts occur during cleanup when multiple tests dispose simultaneously
- All conflicts target the same entity (of:baedr...) in shared DID space
- Created minimal-conflict-repro.test.ts documenting the behavior

The test file includes:
- Detailed explanation of root cause
- Example error output
- Instructions for observing the conflicts
- 20 parallel test instances (requires full suite timing to reproduce)

* docs: Add Deno setup and SSL certificate troubleshooting to DEVELOPMENT.md

- Added Environment Setup section with Deno installation instructions
- Documented PATH configuration for ~/.deno/bin
- Added troubleshooting for SSL certificate errors in CI/test environments
- Included warning about --unsafely-ignore-certificate-errors flag

* docs: Expand SSL certificate troubleshooting with root cause and proper fixes

- Explain root cause: missing/outdated CA certificate bundles
- Add proper fix: installing ca-certificates for Debian/Ubuntu/Alpine
- Document environment variable workarounds (DENO_TLS_CA_STORE, NODE_TLS_REJECT_UNAUTHORIZED)
- Clarify when workarounds are acceptable vs proper fixes

* docs: Simplify SSL certificate section to only document proper fix

Removed workarounds that bypass certificate validation.
Only document the correct solution: installing ca-certificates.

* Revert: Remove incorrect minimal conflict reproduction test

The test was based on incorrect understanding of the issue.

---------

Co-authored-by: Claude <[email protected]>

Author: seefeldb

docs/common/DEVELOPMENT.md

@@ -316,6 +316,47 @@ export const set = (cache: Cache, key: string, value: string) =>
 
 ## Build & Test
 
+### Environment Setup
+
+#### Installing Deno
+
+If Deno is not installed, install it using the official installer:
+
+```bash
+curl -fsSL https://deno.land/install.sh | sh
+```
+
+This installs Deno to `~/.deno/bin/deno`. Add it to your PATH:
+
+```bash
+export PATH="$HOME/.deno/bin:$PATH"
+```
+
+For persistent configuration, add this to your shell profile (`~/.bashrc`, `~/.zshrc`, etc.).
+
+#### SSL Certificate Issues
+
+In some CI/test environments, you may encounter SSL certificate errors when Deno downloads npm packages:
+
+```
+error: Failed caching npm package: invalid peer certificate: UnknownIssuer
+```
+
+This occurs when the system's CA (Certificate Authority) certificate bundle is missing or outdated. Install/update CA certificates on your system:
+
+```bash
+# Debian/Ubuntu
+sudo apt-get update && sudo apt-get install -y ca-certificates
+
+# Alpine Linux (common in Docker containers)
+apk add --no-cache ca-certificates
+
+# Update certificate store
+sudo update-ca-certificates
+```
+
+### Running Tests
+
 - Check typings with `deno task check`.
 - Run linter with `deno lint`.
 - Run all tests using `deno task test` (NOT `deno test`)