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/gemini_response.h

@@ -0,0 +1,23 @@
+#pragma once
+
+#include <string>
+
+namespace roro::gemini {
+
+enum class Category { Input, Success, Redirect, TemporaryFailure, PermanentFailure, ClientCertificate, Unknown };
+
+// The response header: "<two digits> <meta>", at most 1024 bytes of meta.
+struct Header {
+    int status = 0;
+    std::string meta;
+
+    Category category() const;
+    bool sensitiveInput() const { return status == 11; }
+    // 2x: the MIME type, lower-cased, without parameters ("text/gemini" when meta is empty).
+    std::string mimeType() const;
+    std::string parameter(const std::string& name) const;  // e.g. "charset"
+};
+
+bool parseHeader(const std::string& line, Header& out);
+
+}  // namespace roro::gemini