Customizable ports (#962)

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## High-level PR Summary

This PR changes the default development ports for several background
services to avoid conflicts. PostgreSQL moves from port `5432` to
`8128`, Inbucket SMTP from `2500` to `8129`, Inbucket POP3 from `1100`
to `8130`, and the OpenTelemetry collector from `4318` to `8131`. All
references across configuration files, Docker Compose setups,
environment files, CI/CD workflows, test files, and documentation have
been updated to reflect these new port assignments. A knowledge base
document has been added to document the new port mappings.

⏱️ Estimated Review Time: 15-30 minutes

<details>
<summary>💡 Review Order Suggestion</summary>

| Order | File Path |
| --- | --- |
| 1 | `claude/CLAUDE-KNOWLEDGE.md` |
| 2 | `apps/dev-launchpad/public/index.html` |
| 3 | `docker/dependencies/docker.compose.yaml` |
| 4 | `docker/emulator/docker.compose.yaml` |
| 5 | `apps/backend/.env` |
| 6 | `apps/backend/.env.development` |
| 7 | `docker/server/.env.example` |
| 8 | `package.json` |
| 9 | `.devcontainer/devcontainer.json` |
| 10 | `apps/e2e/.env.development` |
| 11 | `.github/workflows/check-prisma-migrations.yaml` |
| 12 | `.github/workflows/docker-server-test.yaml` |
| 13 | `.github/workflows/e2e-api-tests.yaml` |
| 14 | `.github/workflows/e2e-source-of-truth-api-tests.yaml` |
| 15 | `.github/workflows/restart-dev-and-test.yaml` |
| 16 |
`apps/e2e/tests/backend/endpoints/api/v1/internal/email-drafts.test.ts`
|
| 17 | `apps/e2e/tests/backend/endpoints/api/v1/internal/email.test.ts`
|
| 18 | `apps/e2e/tests/backend/endpoints/api/v1/send-email.test.ts` |
| 19 |
`apps/e2e/tests/backend/endpoints/api/v1/unsubscribe-link.test.ts` |
| 20 | `apps/e2e/tests/backend/workflows.test.ts` |
| 21 | `docs/templates/others/self-host.mdx` |

</details>

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----

> [!IMPORTANT]
> This PR introduces customizable development ports using
`NEXT_PUBLIC_STACK_PORT_PREFIX`, updating configurations, documentation,
and tests accordingly.
> 
>   - **Behavior**:
> - Default development ports for services are now customizable via
`NEXT_PUBLIC_STACK_PORT_PREFIX`.
> - PostgreSQL port changed from `5432` to
`${NEXT_PUBLIC_STACK_PORT_PREFIX:-81}28`.
> - Inbucket SMTP port changed from `2500` to
`${NEXT_PUBLIC_STACK_PORT_PREFIX:-81}29`.
> - Inbucket POP3 port changed from `1100` to
`${NEXT_PUBLIC_STACK_PORT_PREFIX:-81}30`.
> - OpenTelemetry collector port changed from `4318` to
`${NEXT_PUBLIC_STACK_PORT_PREFIX:-81}31`.
>   - **Configuration**:
> - Updated `docker.compose.yaml` to use new port variables for services
like PostgreSQL, Inbucket, and OpenTelemetry.
> - Environment files in `apps/backend`, `apps/dashboard`, and
`apps/e2e` updated to use `NEXT_PUBLIC_STACK_PORT_PREFIX`.
> - `package.json` scripts updated to reflect new port configurations.
>   - **Documentation**:
>     - Added `CLAUDE-KNOWLEDGE.md` to document new port mappings.
>     - Updated `self-host.mdx` to reflect new port configurations.
>   - **Testing**:
> - Updated test files in `apps/e2e/tests` to use new port
configurations.
>     - Added `helpers/ports.ts` for port-related utilities in tests.
> 
> <sup>This description was created by </sup>[<img alt="Ellipsis"
src="https://img.shields.io/badge/Ellipsis-blue?color=175173">](https://www.ellipsis.dev?ref=stack-auth%2Fstack-auth&utm_source=github&utm_medium=referral)<sup>
for 76ef55f58f. You can
[customize](https://app.ellipsis.dev/stack-auth/settings/summaries) this
summary. It will automatically update as commits are pushed.</sup>

----


<!-- ELLIPSIS_HIDDEN -->

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

- **New Features**
- Enable configurable development ports via a
NEXT_PUBLIC_STACK_PORT_PREFIX, allowing parallel local environments with
custom port prefixes.

- **Bug Fixes**
- Updated local service port mappings and CI/workflow settings so
tooling and tests use the new prefixed ports consistently.

- **Documentation**
- Added docs and contributor guidance for running multiple parallel
workspaces with custom port prefixes.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Co-authored-by: N2D4 <[email protected]>

.devcontainer/devcontainer.json

@@ -14,10 +14,6 @@
     "memory": "16gb"
   },
   "forwardPorts": [
-    5432,   // PostgreSQL
-    2500,   // Inbucket SMTP
-    1100,   // Inbucket POP3
-    4318,   // OTel collector
     8100, 8101, 8102, 8103, 8104, 8105, 8106, 8107, 8108, 8109,
     8110, 8111, 8112, 8113, 8114, 8115, 8116, 8117, 8118, 8119,
     8120, 8121, 8122, 8123, 8124, 8125, 8126, 8127, 8128, 8129,