chore(docs): answer the self-hosting question explicitly

## Problem
`docs/license.mdx` says the source licence is *"separate from the Personal, Pro
Business, API Starter, API Business, and Enterprise licenses that govern use of
the hosted Service and its outputs"* — but **never states whether self-hosting
requires a subscription**, or what is gated server-side.

`SELF_HOSTING.md` gives a full docker/podman-compose quick start,
secret generation and `./scripts/run-seeders.sh`, so self-hosting clearly works.

## Why it matters
Kal asked, almost verbatim: *"could we modify and add it as a modular so we can
add our own modules to it?"* — and was told "theoretically you can rebuild it
from scratch, it's open source." A technical evaluator at an AGPL project **will**
ask "what stops me self-hosting this instead of paying?"

The answer is presumably that self-hosting gets the code but not our data
pipeline, API keys, or seeded caches — but that is nowhere stated, so the
question hangs.

## Fix
A clear docs page: what self-hosting gives you, what it does not, what requires
a commercial licence, what AGPL obligations attach if you modify and serve it,
and the honest cost comparison (running 500+ seeders is not free).

Being straightforward here **increases** conversion. The gap between "you can
self-host" and "here is exactly what that costs you" is where an evaluator
invents a worse answer than the truth.

## Acceptance
- [ ] Self-hosting scope documented — what is and is not included
- [ ] AGPL obligations explained plainly
- [ ] Commercial licence trigger stated
- [ ] Honest operational cost comparison

Related: #5415 — self-hosted Docker returns HTTP 401 on
`/api/intelligence/v1/get-country-intel-brief` before the handler runs. That is
the concrete version of this question and should be answered in the same doc.
Effort: M (~2d).

Start with docs/license.mdx and SELF_HOSTING.md, then review related issue #5415 for the self-hosted API behavior. Confirm the self-hosting scope, AGPL obligations, commercial-license trigger, and operational cost with maintainers before documenting them. Done means the page answers each acceptance item plainly and links to the relevant setup or licensing guidance.

Written by the indexing model from the issue text.