Add end-agency enrichment and the channel/pricing confidentiality rule

Bryan, two related requests:

1. When a topic has a real end-client agency, the skill should resolve
   its full identity -- not just whatever name got said in the meeting.
   Added as a new standing step: check the MPM Technical Reference
   System first (agency-roster.md, clients-and-partners.md -- cheap,
   already-vetted), fall back to public web research, resolve BOTH the
   legal entity name and the separate transit brand name distinctly
   (validated pattern, confirmed against MPM's own FTA filings for
   Oshkosh: 'City of Oshkosh, Wisconsin, dba: GO Transit'), re-host the
   logo as a data URI rather than hotlinking it, and capture general
   agency contact info. Gets its own 'End Agency' card, separate from
   individual attendees.

2. Pricing shown in the Oshkosh brief was correct for an internal
   audience, but Bryan flagged that an external-facing version must
   never show the end agency MPM's price to the reseller -- they aren't
   privy to it. Documented as a new Hard Rule, grounded directly in the
   Technical Reference System's own reseller-channel.md (MPM's contract
   of record is with the reseller, not the agency, on channel accounts)
   rather than invented from scratch. Doesn't change internal-meeting-
   brief's current behavior (it's internal by definition) -- recorded
   here as the binding rule for vendor-partner-brief and kickoff-brief's
   external-client variant, neither built yet.

skills/internal-meeting-brief/references/section-structure.md

@@ -18,6 +18,11 @@ structure per meeting. This is the contract — read it before generating a brie
    When external counterparts are named in discussion but weren't present, give them
    their own card group ("Named in discussion, not present") with resolved contact
    info (see SKILL.md step 4) rather than omitting them or burying them in prose.
+   **If the topic has a real end-client organization** (an agency, most commonly),
+   give it a distinct "End Agency" card of its own — separate from individual
+   people — showing the legal-name/brand-name pair (e.g. "City of Oshkosh, dba: GO
+   Transit"), a re-hosted logo, website, and general contact info. See SKILL.md
+   step 5.
 3. **Topics Covered** — a `cards` grid, one card per distinct subject actually
    discussed. Card count and grid density (c2/c3/c4) follow the number of real topics —
    don't pad to hit a round number, don't force unrelated topics into one card to save