profile: fix heading hierarchy, add a dark-mode mark, drop the nbsp crutch

profile/README.md

@@ -1,8 +1,22 @@
+<!-- The h1 sits below the brand lockup by design: the mark leads the hero.
+     The a11y requirement MD041 protects — a top-level heading naming the
+     document — is satisfied at "# Answers with receipts" below. MD041 stays
+     enforced for every other file in the repo. -->
+<!-- markdownlint-disable-next-line MD041 -->
 <div align="center">
 
-<img alt="citature — answers with receipts" src="https://raw.githubusercontent.com/citature/.github/main/profile/assets/mark.svg" width="112" height="112">
+<picture>
+  <source
+    media="(prefers-color-scheme: dark)"
+    srcset="https://raw.githubusercontent.com/citature/.github/main/profile/assets/mark-dark.svg">
+  <img
+    alt="citature"
+    src="https://raw.githubusercontent.com/citature/.github/main/profile/assets/mark.svg"
+    width="112"
+    height="112">
+</picture>
 
-### Answers with receipts
+# Answers with receipts
 
 **Agent-native tools over public US federal records.**
 
@@ -11,24 +25,26 @@ upstream government source, retrieval timestamps, coverage caveats, and match
 provenance on every cross-source join. Nothing is asserted without a locator you
 can re-fetch yourself.
 
-[citature.com](https://citature.com) &nbsp;·&nbsp; [Apify Store](https://apify.com/citature)
+[citature.com](https://citature.com) · [Apify Store](https://apify.com/citature)
 
 </div>
 
 ---
 
-### The data &nbsp;·&nbsp; primary sources only
+## The data
 
-Public-domain US federal records, refreshed nightly from the source of record —
-never an aggregator.
+Primary sources only. Public-domain US federal records, refreshed nightly from
+the source of record — never an aggregator.
 
 - **FEC** — campaign finance: 217M+ itemized contribution records across the
   2020–2026 cycles, plus committees and candidates
 - **USASpending** — federal awards and contracts, keyed on recipient UEI
 - **SAM.gov** — contract opportunities and solicitations
 - **Grants.gov** — grant opportunities
 
-### The tools &nbsp;·&nbsp; on [Apify Store](https://apify.com/citature)
+## The tools
+
+Delivered on the [Apify Store](https://apify.com/citature).
 
 - **Money** — FEC contributions by state and committee type, federal awards by
   agency/state/recipient, follow-the-money committee inflows, and funding-entity
@@ -37,7 +53,7 @@ never an aggregator.
   contractor award lineage by agency, and agency buying patterns by year
 - **MCP** — every tool above delivered as agent-native calls from one MCP server
 
-### The rules
+## The rules
 
 Research over public records — never legal, financial, or eligibility advice.
 Entity-level data only; no individual-person products. citature reports what the
@@ -46,5 +62,8 @@ record says and never renders a verdict.
 ---
 
 <div align="center">
-  <sub><b><a href="https://citature.com">citature.com</a></b> &nbsp;·&nbsp; answers with receipts, from primary sources</sub>
+  <sub>
+    <b><a href="https://citature.com">citature.com</a></b>
+    · answers with receipts, from primary sources
+  </sub>
 </div>