fix(windows): native ConPTY + kernel32 metrics + agent loop cap (v0.7.6)

Three issues reported on Windows + one user-requested limit bump:

1. Dashboard CPU/RAM/Network all at 0
   handleSystemMetrics read /proc/* exclusively. Replaced with a
   platform-split:
   - metrics_unix.go (!windows): existing /proc reading code.
   - metrics_windows.go: kernel32!GetSystemTimes for CPU
     (delta of idle vs kernel+user FILETIMEs) and
     kernel32!GlobalMemoryStatusEx for memory. Network left at zero
     for now — MIB_IF_ROW2 is too version-sensitive to parse by hand.
   handlers_info.go::handleSystemMetrics reduced to one delegating
   call.

2. Terminal black screen on Windows
   creack/pty/v2 returns "unsupported" on Windows; the v0.7.1 pipe
   fallback works but pipes don't carry TTY signals, so cmd/pwsh/wsl
   go silent. Implemented native ConPTY:
   - terminal_conpty_windows.go: CreatePseudoConsole + STARTUPINFOEX
     + PROC_THREAD_ATTRIBUTE_PSEUDOCONSOLE wiring via
     windows.NewProcThreadAttributeList. CreateProcessW launches
     child with the PC attached, full ANSI / line discipline /
     resize.
   - canUseConPTY() probes once at startup (Win10 1809+ check).
   - Restructure: terminal_session.go now holds just the interface
     + ptySession + pipeSession structs. terminal_session_unix.go
     wires creack/pty. terminal_session_windows.go tries ConPTY
     first, falls back to pipeSession.

3. Agent stops after 15 tool calls
   MaxToolIterations bumped 15 → 500. Doc comment explains why the
   cap exists at all (infinite-loop safety) and that 500 is well
   above realistic usage.

- internal/version/version.go: 0.7.5 → 0.7.6
- CHANGELOG.md: v0.7.6 entry covers the three fixes

internal/api/terminal_session.go

@@ -2,19 +2,22 @@ package api
 
 // Cross-platform terminal session abstraction.
 //
-// On Linux / macOS we have a real PTY via creack/pty: full TTY semantics,
-// resize support, interactive apps (vim, top…) work. On Windows the same
-// package returns "operating system not supported" at pty.Start time, so we
-// fall back to plain pipes (stdin / stdout merged with stderr). Pipes don't
-// give a real TTY — interactive TUIs misbehave — but `wsl`, `pwsh`, `cmd`,
-// and most CLI tools emit usable line-buffered output, which is what the
-// user actually clicks for.
+// On Linux / macOS the unix-tagged file (terminal_session_unix.go) wires
+// startTermSession to creack/pty for a real PTY: full TTY semantics,
+// resize support, interactive apps (vim, top…) work.
+//
+// On Windows the windows-tagged file (terminal_session_windows.go) tries
+// the kernel32 ConPTY API first, with a pipe-based fallback for older
+// hosts. pipeSession does NOT carry TTY signals, so most shells go silent
+// — it's only kept as a last resort.
+//
+// Both platforms share the termSession interface, the ptySession type
+// (used by unix), and the pipeSession type (used by the Windows fallback).
 
 import (
 	"io"
 	"os"
 	"os/exec"
-	"runtime"
 	"sync"
 
 	"github.com/creack/pty/v2"
@@ -30,22 +33,7 @@ type termSession interface {
 	Pid() int
 }
 
-// startTermSession tries a real PTY first; on Windows or any pty.Start failure
-// it falls back to a pipe-based session.
-func startTermSession(cmd *exec.Cmd) (termSession, error) {
-	if runtime.GOOS != "windows" {
-		ptmx, err := pty.Start(cmd)
-		if err == nil {
-			return &ptySession{ptmx: ptmx, cmd: cmd}, nil
-		}
-		// On unix, a pty.Start error is fatal — pipes won't help interactive
-		// shells without a TTY, and the unix build is the supported path.
-		return nil, err
-	}
-	return startPipeSession(cmd)
-}
-
-// ptySession wraps creack/pty's *os.File-backed PTY.
+// ptySession wraps creack/pty's *os.File-backed PTY (unix path).
 type ptySession struct {
 	ptmx *os.File
 	cmd  *exec.Cmd
@@ -76,8 +64,10 @@ func (s *ptySession) Pid() int {
 	return s.cmd.Process.Pid
 }
 
-// pipeSession is the Windows fallback: stdin pipe + merged stdout/stderr pipe,
-// running concurrently. Resize is a no-op (no TTY to send TIOCSWINSZ to).
+// pipeSession is the Windows last-resort fallback when ConPTY is not
+// available: stdin pipe + merged stdout/stderr, no TTY signals. Most
+// interactive shells go silent in this mode, so it should rarely be hit on
+// modern Windows (10 1809+).
 type pipeSession struct {
 	cmd     *exec.Cmd
 	stdin   io.WriteCloser
@@ -115,7 +105,7 @@ func startPipeSession(cmd *exec.Cmd) (termSession, error) {
 		cmd:     cmd,
 		stdin:   stdin,
 		stdout:  stdout,
-		stderr: stderr,
+		stderr:  stderr,
 		merged:  make(chan []byte, 32),
 		closeCh: make(chan struct{}),
 	}