feat: P5 — replace E2E platform skip lists with capability-based tags

Each test now declares requirements via `# requires:` comment.
run_all.sh detects available capabilities (elf, gcc, symlink,
scan-deps, import-std-libcxx, etc.) and skips tests with
missing requirements — no more platform-specific skip arrays.

Author: Sunrisepeak

tests/e2e/01_help_and_version.sh

@@ -1,4 +1,5 @@
 #!/usr/bin/env bash
+# requires:
 # Verify --help and --version
 set -e
 

tests/e2e/02_new_build_run.sh

@@ -1,4 +1,5 @@
 #!/usr/bin/env bash
+# requires:
 # Single-module hello world: mcpp new → build → run
 set -e
 

tests/e2e/03_multi_module.sh

@@ -1,4 +1,5 @@
 #!/usr/bin/env bash
+# requires: elf gcc
 # Multi-module: package with .cppm + main.cpp importing it
 set -e
 

tests/e2e/04_incremental.sh

@@ -1,4 +1,5 @@
 #!/usr/bin/env bash
+# requires:
 # Incremental: a no-op rebuild does no work; touching main.cpp recompiles only it
 set -e
 

tests/e2e/05_errors.sh

@@ -1,4 +1,5 @@
 #!/usr/bin/env bash
+# requires:
 # Error paths: missing manifest, missing version, conditional import, header unit, naming violation
 set -e
 

tests/e2e/06_emit_xpkg.sh

@@ -1,4 +1,5 @@
 #!/usr/bin/env bash
+# requires:
 # emit xpkg: produce valid Lua entry from mcpp.toml
 set -e
 

tests/e2e/07_static_library.sh

@@ -1,4 +1,5 @@
 #!/usr/bin/env bash
+# requires: elf
 # Static library: kind = "lib"  → libNAME.a via `ar rcs`
 set -e
 

tests/e2e/08_shared_library.sh

@@ -1,4 +1,5 @@
 #!/usr/bin/env bash
+# requires: elf
 # Shared library: kind = "shared" → libNAME.so via -shared -fPIC
 set -e
 

tests/e2e/09_path_dependency.sh

@@ -1,4 +1,5 @@
 #!/usr/bin/env bash
+# requires: elf gcc
 # Path-based dependency: package B imports modules from package A via
 #   [dependencies.A] path = "../A"
 # Verifies the multi-package scanner + linker pipeline.

tests/e2e/10_env_command.sh

@@ -1,4 +1,5 @@
 #!/usr/bin/env bash
+# requires: symlink
 # `mcpp env` initializes $MCPP_HOME and prints expected layout.
 set -e