G1 step 2: Gemini parsers (host-tested), and the memory decision (Q86)

lib/gemini: URLs split per RFC 3986 appendix B and resolved per section
5.2 (all 32 reference examples of 5.4 pass, with gemini:// for http://),
the request form (no fragment, lower-case host, never an empty path),
query encoding for input prompts, Saved Page paths; the response header
(status, category, MIME type and parameters, 1024-byte meta limit);
gemtext's line types; and display text for the Latin-1 fonts. 12 tests.

Q86, decided after step 1: free heap stays above 40 KB in steady state
and 20 KB during a handshake; a fetch won't start below 55 KB.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EhqxQ49eCju4CzKYNjZzwT

lib/gemini/src/gemtext.h

@@ -0,0 +1,23 @@
+#pragma once
+
+#include <string>
+#include <vector>
+
+namespace roro::gemini {
+
+enum class LineType { Text, Link, Heading1, Heading2, Heading3, ListItem, Quote, PreToggle, Preformatted };
+
+// One gemtext line. Link: `url` and its label in `text` (the URL itself without a label).
+// PreToggle: the ``` line, with its alt text. Preformatted: kept exactly.
+struct GemLine {
+    LineType type = LineType::Text;
+    std::string text, url;
+};
+
+std::vector<GemLine> parseGemtext(const std::string& document);
+
+// For the Latin-1 fonts (Q79): valid UTF-8 up to U+00FF kept, anything else '?', and tabs
+// expanded to 4-column stops.
+std::string displayText(const std::string& utf8);
+
+}  // namespace roro::gemini