refactor(deeplink): split monolithic deeplink.rs into modular structure

Split the 1691-line deeplink.rs into a well-organized module directory:

- mod.rs (120 lines): DeepLinkImportRequest struct and public exports
- parser.rs (321 lines): URL parsing logic for all resource types
- provider.rs (510 lines): Provider import and config merge logic
- mcp.rs (191 lines): MCP server batch import
- prompt.rs (86 lines): Prompt import
- skill.rs (52 lines): Skill repository import
- utils.rs (99 lines): Shared utilities (URL validation, Base64 decoding)
- tests.rs (384 lines): All unit tests

Benefits:
- Max file size reduced from 1691 to 510 lines
- Each resource type has its own import module
- Shared utilities extracted for reuse
- All 17 deeplink tests + 107 total tests passing

src-tauri/src/deeplink/utils.rs

@@ -0,0 +1,99 @@
+//! Deep link utility functions
+//!
+//! Common helpers for URL validation, Base64 decoding, etc.
+
+use crate::error::AppError;
+use base64::prelude::*;
+use url::Url;
+
+/// Validate that a string is a valid HTTP(S) URL
+pub fn validate_url(url_str: &str, field_name: &str) -> Result<(), AppError> {
+    let url = Url::parse(url_str)
+        .map_err(|e| AppError::InvalidInput(format!("Invalid URL for '{field_name}': {e}")))?;
+
+    let scheme = url.scheme();
+    if scheme != "http" && scheme != "https" {
+        return Err(AppError::InvalidInput(format!(
+            "Invalid URL scheme for '{field_name}': must be http or https, got '{scheme}'"
+        )));
+    }
+
+    Ok(())
+}
+
+/// Decode a Base64 parameter from deep link URL
+///
+/// This function handles common issues with Base64 in URLs:
+/// - `+` being decoded as space
+/// - Missing padding `=`
+/// - Both standard and URL-safe Base64 variants
+pub fn decode_base64_param(field: &str, raw: &str) -> Result<Vec<u8>, AppError> {
+    let mut candidates: Vec<String> = Vec::new();
+    // Keep spaces (to restore `+`), but remove newlines
+    let trimmed = raw.trim_matches(|c| c == '\r' || c == '\n');
+
+    // First try restoring spaces to "+"
+    if trimmed.contains(' ') {
+        let replaced = trimmed.replace(' ', "+");
+        if !replaced.is_empty() && !candidates.contains(&replaced) {
+            candidates.push(replaced);
+        }
+    }
+
+    // Original value
+    if !trimmed.is_empty() && !candidates.contains(&trimmed.to_string()) {
+        candidates.push(trimmed.to_string());
+    }
+
+    // Add padding variants
+    let existing = candidates.clone();
+    for candidate in existing {
+        let mut padded = candidate.clone();
+        let remainder = padded.len() % 4;
+        if remainder != 0 {
+            padded.extend(std::iter::repeat_n('=', 4 - remainder));
+        }
+        if !candidates.contains(&padded) {
+            candidates.push(padded);
+        }
+    }
+
+    let mut last_error: Option<String> = None;
+    for candidate in candidates {
+        for engine in [
+            &BASE64_STANDARD,
+            &BASE64_STANDARD_NO_PAD,
+            &BASE64_URL_SAFE,
+            &BASE64_URL_SAFE_NO_PAD,
+        ] {
+            match engine.decode(&candidate) {
+                Ok(bytes) => return Ok(bytes),
+                Err(err) => last_error = Some(err.to_string()),
+            }
+        }
+    }
+
+    Err(AppError::InvalidInput(format!(
+        "{field} 参数 Base64 解码失败：{}。请确认链接参数已用 Base64 编码并经过 URL 转义（尤其是将 '+' 编码为 %2B，或使用 URL-safe Base64）。",
+        last_error.unwrap_or_else(|| "未知错误".to_string())
+    )))
+}
+
+/// Infer homepage URL from API endpoint
+///
+/// Examples:
+/// - https://api.anthropic.com/v1 → https://anthropic.com
+/// - https://api.openai.com/v1 → https://openai.com
+/// - https://api-test.company.com/v1 → https://company.com
+pub fn infer_homepage_from_endpoint(endpoint: &str) -> Option<String> {
+    let url = Url::parse(endpoint).ok()?;
+    let host = url.host_str()?;
+
+    // Remove common API prefixes
+    let clean_host = host
+        .strip_prefix("api.")
+        .or_else(|| host.strip_prefix("api-"))
+        .unwrap_or(host);
+
+    Some(format!("https://{clean_host}"))
+}