modules: split services and the ircd link into external crates

nickserv, chanserv and the InspIRCd protocol move out of the binary into their
own workspace crates (fedserv-nickserv, fedserv-chanserv, fedserv-inspircd),
each depending only on fedserv-api. human_time and the branded account emails
move into the SDK crate so a module needs nothing from core; the engine keeps
its own inherent methods and builds emails via fedserv-api too. The bin now
constructs each module from its crate instead of an in-tree #[path] include.
Proves the SDK is self-sufficient: a third-party module is the same shape.

api/src/email.rs

@@ -0,0 +1,76 @@
+// Email content: renders the HTML templates in ../templates/email and pairs each
+// with a plaintext fallback. The link layer sends both as multipart/alternative.
+
+pub struct Mail {
+    pub subject: String,
+    pub text: String,
+    pub html: String,
+}
+
+const BASE: &str = include_str!("../templates/email/base.html");
+
+// The masthead: a logo image beside the brand name when a logo URL is set,
+// otherwise the brand name as an accent eyebrow.
+fn brand_mark(brand: &str, accent: &str, logo: &str) -> String {
+    let (brand, accent) = (escape(brand), escape(accent));
+    if logo.is_empty() {
+        format!("<span style=\"font-size:12px;font-weight:700;letter-spacing:1.6px;text-transform:uppercase;color:{accent};\">{brand}</span>")
+    } else {
+        format!(
+            "<img src=\"{}\" width=\"40\" height=\"40\" alt=\"\" style=\"display:inline-block;border-radius:9px;vertical-align:middle;\"><span style=\"display:inline-block;margin-left:12px;vertical-align:middle;font-size:18px;font-weight:800;letter-spacing:.2px;color:#0f172a;\">{brand}</span>",
+            escape(logo)
+        )
+    }
+}
+
+fn render(brand: &str, accent: &str, logo: &str, title: &str, message: &str, code: &str, note: &str) -> String {
+    BASE.replace("{{brand_mark}}", &brand_mark(brand, accent, logo))
+        .replace("{{brand}}", &escape(brand))
+        .replace("{{accent}}", &escape(accent))
+        .replace("{{title}}", &escape(title))
+        .replace("{{message}}", &escape(message))
+        .replace("{{code}}", &escape(code))
+        .replace("{{note}}", &escape(note))
+}
+
+pub fn reset(brand: &str, accent: &str, logo: &str, account: &str, code: &str) -> Mail {
+    Mail {
+        subject: format!("Password reset for {account}"),
+        text: format!(
+            "Your password reset code for {account} is: {code}\nIt expires in 15 minutes.\nReset with:\n  /msg NickServ RESETPASS {account} {code} <newpassword>\n"
+        ),
+        html: render(
+            brand,
+            accent,
+            logo,
+            "Password reset",
+            &format!("Use this code to reset the password for your account {account}."),
+            code,
+            "This code expires in 15 minutes. If you didn't ask to reset it, ignore this email.",
+        ),
+    }
+}
+
+pub fn confirm(brand: &str, accent: &str, logo: &str, account: &str, code: &str) -> Mail {
+    Mail {
+        subject: format!("Confirm your {account} registration"),
+        text: format!(
+            "Confirm your account {account} with:\n  /msg NickServ CONFIRM {code}\nThe code expires in 15 minutes.\n"
+        ),
+        html: render(
+            brand,
+            accent,
+            logo,
+            "Confirm your account",
+            &format!("Welcome! Confirm the email for your account {account} with the code below."),
+            code,
+            "This code expires in 15 minutes.",
+        ),
+    }
+}
+
+// Escape the few characters that matter inside HTML text so a value can't break
+// out of the template.
+fn escape(s: &str) -> String {
+    s.replace('&', "&amp;").replace('<', "&lt;").replace('>', "&gt;")
+}

api/src/lib.rs

@@ -2,6 +2,9 @@
 //! it carries the traits a module implements and the normalized vocabulary the
 //! engine speaks, with no storage or runtime dependencies of its own.
 
+// Branded account emails (confirm / reset), shared by the engine and modules.
+pub mod email;
+
 // ---------------------------------------------------------------------------
 // Protocol vocabulary
 // ---------------------------------------------------------------------------
@@ -448,3 +451,22 @@ fn glob_match(pattern: &str, text: &str) -> bool {
     }
     pi == p.len()
 }
+
+// Format a Unix timestamp (seconds) as "YYYY-MM-DD HH:MM:SS UTC", using Howard
+// Hinnant's civil-from-days algorithm so no date crate is needed.
+pub fn human_time(ts: u64) -> String {
+    let days = (ts / 86400) as i64;
+    let rem = ts % 86400;
+    let (hh, mm, ss) = (rem / 3600, (rem % 3600) / 60, rem % 60);
+    let z = days + 719468;
+    let era = (if z >= 0 { z } else { z - 146096 }) / 146097;
+    let doe = z - era * 146097;
+    let yoe = (doe - doe / 1460 + doe / 36524 - doe / 146096) / 365;
+    let y = yoe + era * 400;
+    let doy = doe - (365 * yoe + yoe / 4 - yoe / 100);
+    let mp = (5 * doy + 2) / 153;
+    let day = doy - (153 * mp + 2) / 5 + 1;
+    let month = if mp < 10 { mp + 3 } else { mp - 9 };
+    let year = y + i64::from(month <= 2);
+    format!("{year:04}-{month:02}-{day:02} {hh:02}:{mm:02}:{ss:02} UTC")
+}