docs: add the full build-session video, count 22 agents, ground resource usage

Add the 2.5-hour 'Working with RoboCo' build session (a conversation to a
shipped feature) as a second hero thumbnail beside the 26-min intro.

Update the agent count from 20 to 22 across the README, CLAUDE.md, usage,
the base agent prompt, the how-to guide, and the org-structure RAG doc:
the standing org gains the PR Reviewer (board-level, read-only), and the
on-demand Intake and Secretary are now counted. The org-structure doc
gains the PR Reviewer in the hierarchy, count table, board team, and
communication matrix. The historical 0.1.0 changelog entry is left as-is.

Rewrite the resource-usage section: drop the unmeasured per-agent RAM
ceiling (RAM is low and agents run few-at-a-time) and lead with storage —
the image set's shared base layer — which is what docker prune reclaims.

docs/how-to.md

@@ -2,7 +2,7 @@
 
 ![Twelve-second looping preview of the RoboCo control panel — the org tree, a task in progress, and an approval queue.](videos/panel-teaser.gif)
 
-RoboCo is a virtual software company — 20 AI agents and one human: you. Not a
+RoboCo is a virtual software company — 22 AI agents and one human: you. Not a
 swarm of bots, not a framework to wire together — an **organization**, with
 roles, a chain of command, formal reviews, and sign-offs. You don't micromanage
 it; you run it like a CEO. Drop work in at the top and the company carries it all
@@ -10,7 +10,7 @@ the way through planning, building, review, and documentation, then brings it
 back to your desk for the final word. You act at the two ends; the organization
 fills in everything between.
 
-What keeps twenty agents from dissolving into noise is that RoboCo is
+What keeps twenty-two agents from dissolving into noise is that RoboCo is
 relentlessly opinionated about *how* work happens: everything is a task, no task
 moves without acceptance criteria, and every task walks the same strict lifecycle
 — built, QA'd, documented, PM-reviewed, approved — each step gated by role. The
@@ -260,7 +260,7 @@ for a demo — it's a real page RoboCo's agents shipped to RoboCo's own control
 panel. A company building its own product, in front of you, is the whole point of
 RoboCo. What makes that hold together isn't a clever model or a lucky run; it's
 the **organization** — the roles, the gated lifecycle, the reviews and the
-sign-offs that keep twenty agents moving as a company instead of a crowd. Run
+sign-offs that keep twenty-two agents moving as a company instead of a crowd. Run
 as many of these passes as you like, across as many projects as you like.
 
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