docs: drop six unlinked stub files, fold their real content into limits.md

audit-0.7, compatibility, limitations, native, packages and security had
zero inbound links and were titled 'Flint 1.0' with claims the tree does
not back: a native ABI with flint_extension_init, flint.toml package
manifests, TLS certificate validation, concurrency primitives. They were
duplicates of docs/limits.md plus promises.

the two facts only they stated are now in limits.md: no sandbox for
untrusted code, and no bytecode file format, so no untrusted-bytecode
boundary.

Author: programmersd21

docs/README.md

@@ -15,7 +15,7 @@ program you can run: `./flint -e 'print(1)'`.
 | [library.md](library.md) | the built-in functions |
 | [errors.md](errors.md) | what goes wrong, and what flint does |
 | [diagnostics.md](diagnostics.md) | formats, current coverage, and `--fix` |
-| [limits.md](limits.md) | what the language does not do |
+| [limits.md](limits.md) | what the language does not do, and untrusted input |
 | [internals.md](internals.md) | how the compiler and the vm work |
 
 the formal grammar and semantics are in [../SPEC.md](../SPEC.md), and the

docs/audit-0.7.md

@@ -68,7 +68,27 @@ the `flint` executable runs scripts, `-e` code, stdin and the repl, plus
 `lint`, `build`, `debug`, `profile`, `doc`, `package`, `install` or `lsp`
 subcommands.
 
-there is no package manager, no registry and no lockfile. there are no
-threads, channels or locks. the `http` module is a blocking client with no
-tls. there is no cryptography beyond the non-cryptographic `random` module,
-which says so itself.
+there is no package manager, no registry and no lockfile. `flint.toml` is
+not a source format. the only ways to get code into a script are
+`import "some/file.fl"`, an `import` of a standard-library module by name,
+and `flint sync` to refresh the installed library.
+
+there are no threads, channels or locks. the `http` module is a blocking
+client with no tls, so it validates no certificates; do not send secrets
+through it. there is no cryptography beyond the non-cryptographic `random`
+module, which says so itself.
+
+there is no c extension point: no public header, no `native.load`, no
+ownership contract. `vm.h` and friends are internals and change between
+commits.
+
+## untrusted input
+
+flint has no permission system and no sandbox. a script that can run can
+read and write every file its user can. do not run flint programs you have
+not read.
+
+there is no bytecode file format and no loader, so there is no untrusted
+bytecode boundary; all bytecode is produced in-process by the compiler and
+checked by the in-process verifier before it runs. anything that arrives as
+a `.fl` file is source.