feat: add ISR cache with stale-while-revalidate pattern

Implements in-memory caching for SSR pages using moka with:
- Configurable fresh/stale TTLs (60s/300s defaults)
- Background refresh for stale entries
- Cache invalidation on project/tag mutations
- Pre-cached icon collections on startup
- Skips cache for authenticated requests

Cargo.lock

@@ -82,6 +82,7 @@ dependencies = [
  "futures",
  "include_dir",
  "mime_guess",
+ "moka",
  "nu-ansi-term",
  "rand 0.9.2",
  "reqwest",
@@ -113,6 +114,17 @@ dependencies = [
  "password-hash",
 ]
 
+[[package]]
+name = "async-lock"
+version = "3.4.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "290f7f2596bd5b78a9fec8088ccd89180d7f9f55b94b0576823bbbdc72ee8311"
+dependencies = [
+ "event-listener",
+ "event-listener-strategy",
+ "pin-project-lite",
+]
+
 [[package]]
 name = "atoi"
 version = "2.0.0"
@@ -904,6 +916,24 @@ dependencies = [
  "cfg-if",
 ]
 
+[[package]]
+name = "crossbeam-channel"
+version = "0.5.15"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "82b8f8f868b36967f9606790d1903570de9ceaf870a7bf9fbbd3016d636a2cb2"
+dependencies = [
+ "crossbeam-utils",
+]
+
+[[package]]
+name = "crossbeam-epoch"
+version = "0.9.18"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5b82ac4a3c2ca9c3460964f020e1402edd5753411d7737aa39c3714ad1b5420e"
+dependencies = [
+ "crossbeam-utils",
+]
+
 [[package]]
 name = "crossbeam-queue"
 version = "0.3.12"
@@ -1119,6 +1149,16 @@ dependencies = [
  "pin-project-lite",
 ]
 
+[[package]]
+name = "event-listener-strategy"
+version = "0.5.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8be9f3dfaaffdae2972880079a491a1a8bb7cbed0b8dd7a347f668b4150a3b93"
+dependencies = [
+ "event-listener",
+ "pin-project-lite",
+]
+
 [[package]]
 name = "fastrand"
 version = "2.3.0"
@@ -1943,6 +1983,26 @@ dependencies = [
  "windows-sys 0.61.2",
 ]
 
+[[package]]
+name = "moka"
+version = "0.12.12"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a3dec6bd31b08944e08b58fd99373893a6c17054d6f3ea5006cc894f4f4eee2a"
+dependencies = [
+ "async-lock",
+ "crossbeam-channel",
+ "crossbeam-epoch",
+ "crossbeam-utils",
+ "equivalent",
+ "event-listener",
+ "futures-util",
+ "parking_lot",
+ "portable-atomic",
+ "smallvec",
+ "tagptr",
+ "uuid",
+]
+
 [[package]]
 name = "nu-ansi-term"
 version = "0.50.3"
@@ -2143,6 +2203,12 @@ version = "0.3.32"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7edddbd0b52d732b21ad9a5fab5c704c14cd949e5e9a1ec5929a24fded1b904c"
 
+[[package]]
+name = "portable-atomic"
+version = "1.13.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f89776e4d69bb58bc6993e99ffa1d11f228b839984854c7daeb5d37f87cbe950"
+
 [[package]]
 name = "potential_utf"
 version = "0.1.4"
@@ -3103,6 +3169,12 @@ dependencies = [
  "syn",
 ]
 
+[[package]]
+name = "tagptr"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7b2093cf4c8eb1e67749a6762251bc9cd836b6fc171623bd0a9d324d37af2417"
+
 [[package]]
 name = "thiserror"
 version = "1.0.69"